Exercise II on Water Class 6 Concise Chemistry ICSE Solutions

Exercise II on Water

Objective Type Questions

Que-1: Common salt is obtained from sea water by:
(i)distillation
(ii)crystallisation
(iii)evaporation
(iv)sublimation 

Ans- evaporation
Reason- Sea water is allowed to evaporate in shallow salt pans. The water evaporates due to the sun’s heat, leaving behind common salt (sodium chloride).

Que-2: The substance which is insoluble in water :
(i)sugar
(ii)salt
(iii)chalk
(iv)sodium carbonate

Ans- chalk
Reason- Chalk does not dissolve in water, so it is insoluble. Sugar, salt, and sodium carbonate dissolve in water and are therefore soluble.

Que-3: A substance in which another substance is dissolved to form a solution is called:
(i)solute
(ii)solvent
(iii)precipitate
(iv)none of the above

Ans- solvent
Reason- A solvent is the substance in which another substance (the solute) is dissolved to form a solution.

Que-4: The most frequently used solvent is:
(i)water
(ii)alcohol
(iii)vinegar
(iv)carbon disulphite

Ans- water
Reason- Water is called the universal solvent because it dissolves a very large number of substances and is the most commonly used solvent in daily life, laboratories, and industries.

Que-5: The substance which gets dissolved in a solvent to form a solution is called :
(i)solute
(ii)residue
(iii)sediment
(iv)sublimate

Ans- solute
Reason- A solute is the substance that gets dissolved in a solvent to form a solution.

Que-6: The solubility of a solute in a solvent:
(i)increases by stirring
(ii)increases by heating
(iii)depends upon the size of the solute particles
(iv)all of the above

Ans- all of the above
Reason-Stirring, heating, and smaller solute particles help the solute dissolve more easily in the solvent, thereby increasing its solubility.

Short Answer Questions

Que-1: Identify the solute and solvent in the following solutions:
(i) Salt and water
(ii) Iodine and alcohol
(iii) Air and water

Ans- (i) Salt and water
(a)Solute: Salt
(b)Solvent: Water
(ii) Iodine and alcohol
(a)Solute: Iodine
(b)Solvent: Alcohol
(iii) Air and water
(a)Solute: Air
(b)Solvent: Water

Que-2: Define:
(i) Solute
(ii) Solvent
(iii) Solution
(iv) Saturated solution
(v) Unsaturated solution

Ans- (i) Solute: A substance that dissolves in a solvent to form a solution is called a solute.
(ii) Solvent: A substance in which a solute dissolves to form a solution is called a solvent.
(iii) Solution: A homogeneous mixture formed by dissolving a solute in a solvent is called a solution.
(iv) Saturated Solution: A solution that cannot dissolve any more solute at a given temperature is called a saturated solution.
(v) Unsaturated Solution: A solution that can still dissolve more solute at a given temperature is called an unsaturated solution.

Que-3: Why is water called a universal solvent ?

Ans- Water is called a universal solvent because it can dissolve a large number of substances more effectively than any other liquid. It dissolves many solids, liquids, and gases, making it the most commonly used solvent.

Long Answer Questions

Que-1: (i) Define solubility.
(ii) State two factors by which the solubility of a solute in a solvent can be increased.

Ans- (i) Solubility is the maximum amount of a solute that can dissolve in a given quantity of a solvent at a particular temperature to form a saturated solution. It is usually expressed as the number of grams of solute that dissolve in 100 g of solvent.
(ii) (a)Increase in Temperature : For most solid solutes, solubility increases with an increase in temperature. Heating the solvent allows more solute to dissolve.
(b)Stirring : Stirring helps the solute particles come into contact with fresh solvent particles, thereby helping more solute to dissolve and increasing the amount dissolved in a given time.

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Exercise III on Water Class 6 Concise Chemistry ICSE Solutions

Exercise III on Water

Objective Type Questions

Que-1: Chlorination of water is done to :
(i)kill germs
(ii)remove the suspended impurities
(iii)remove the dissolved impurities
(iv)none of the above

Ans- kill germs
Reason-  Chlorination of water is done to kill germs, Water is passed into a chlorination tank to kill all the germs present in it.

Que-2: A method used to kill harmful germs present in water is:
(i)sedimentation
(ii)decantation
(iii)boiling
(iv)filtration

Ans- boiling
Reason- Boiling kills harmful germs and makes water safe for drinking.

Que-3: Sea water is not fit for drinking because it contains a large amount of:
(i)suspended impurities
(ii)sugar
(iii)dissolved salts
(iv)none of the above

Ans- dissolved salts
Reason- Sea water contains a large amount of dissolved salts, which make it unfit for drinking.

Que-4: The gas which adds taste to water is:
(i)oxygen
(ii)nitrogen
(iii)hydrogen
(iv)carbon dioxide

Ans- carbon dioxide
Reason- Carbon dioxide dissolved in water gives it a pleasant taste.

Que-5: Distilled water is:
(i)salty
(ii)sweet
(iii)sour
(iv)tasteless

Ans- tasteless
Reason- Distilled water is free from dissolved salts and gases, so it has no taste.

Que-6: Which of the following is a water-borne disease?
(i)Influenza
(ii)Typhoid
(iii)COVID-19
(iv)Malaria

Ans- Typhoid
Reason- Typhoid spreads through contaminated water and food, so it is a water-borne disease.

Short Answer Questions

Que-1: Name:
(i) Two chemicals used to destroy germs present in water.
(ii) Two diseases which spread through impure water.
(iii) A chemical used for loading.
(iv) Two substances which add taste to water.
(v) Two household methods to get safe drinking water.

Ans- (i) Chlorine and Potassium permanganate
(ii) Typhoid and Cholera
(iii) Alum (Potash alum)
(iv) Oxygen and Carbon dioxide
(v) Boiling and Filtration

Que-2: Define:
(i) Sterilisation
(ii) Sedimentation
(iii) Loading
(iv) Aeration

Ans- (i) Sterilisation: The process of destroying harmful germs present in water to make it safe for drinking is called sterilisation.
(ii) Sedimentation: The process by which heavier insoluble impurities settle down at the bottom of water when it is left undisturbed is called sedimentation.
(iii) Loading: The process of adding alum to water to make fine suspended impurities settle down faster is called loading.
(iv) Aeration: The process of mixing air with water to improve its taste and remove unpleasant odours is called aeration

Que-3: What is the taste of distilled water? Why is it not potable ?

Ans- Distilled water is tasteless. Distilled water is not considered potable for regular drinking because it lacks dissolved minerals and gases such as oxygen and carbon dioxide, which give water its pleasant taste and make it more suitable for drinking. It is mainly used in laboratories, batteries, and scientific work.

Que-4: Answer in brief:
(i) Why is river water unfit for drinking ?
(ii) Why is tap water a mixture ?
(iii) What is mineral water?
(iv) What is the purpose of adding bleaching powder to water supplied to the town?
(v) How is chemically pure water obtained in the laboratory?
(vi) How is water in a swimming pool kept free from germs?
(vii) Why is water important for plants and animals?

Ans- (i) River water contains suspended impurities, dissolved salts, and disease-causing germs, so it is unfit for drinking without treatment.
(ii) Tap water contains dissolved salts, minerals, gases, and other impurities mixed with water, so it is a mixture.
(iii) Mineral water is purified drinking water that contains dissolved minerals beneficial to health.
(vi) Bleaching powder is added to destroy harmful germs and make the water safe for drinking.
(v) Chemically pure water is obtained by the process of distillation.
(vi) Water in a swimming pool is kept free from germs by adding chlorine.
(vii) Water is essential for life. It is needed for various life processes such as digestion, transportation of nutrients, excretion, and photosynthesis in plants.

Long Answer Questions

Que-1: Name the steps involved in the purification of drinking water supplied in cities and towns.

Ans- The water supplied to cities and towns is purified in water treatment plants before it reaches our homes. The main steps are:

(i)Sedimentation: Water is stored in large tanks where heavy insoluble impurities like sand, mud, and pebbles settle at the bottom.
(ii)Loading: Alum is added to water. It causes fine suspended impurities to clump together and settle down quickly.
(iii)Filtration: The clear water is passed through layers of sand and gravel filters to remove remaining suspended particles.
(iv)Sterilisation : Chlorine or bleaching powder is added to the filtered water to kill harmful germs and bacteria.
(v)Storage and Distribution: The purified water is stored in reservoirs and then supplied through pipelines to homes, schools, and other buildings.

Que-2: Give reason:
(i)Ice floats on water.
(ii)Marine life is able to survive in colder regions.
(iii)Water droplets can be seen outside a chilled water bottle.

Ans- (i) Ice floats on water because ice is less dense than water. When water freezes, it expands and its density decreases.
(ii) Marine life can survive in colder regions because water freezes only at the surface. The layer of ice floats on water and acts as an insulator, keeping the water below in the liquid state where aquatic organisms can live.
(iii) Water droplets are seen outside a chilled water bottle because water vapour present in the air condenses on the cold surface of the bottle, forming tiny droplets of water.

Que-3: What is potable water? List four characteristics of potable water.

Ans- Potable water is water that is safe and fit for drinking and domestic use. It does not contain harmful germs or harmful amounts of impurities.
Characteristics of Potable Water
(i)Free from disease-causing germs such as bacteria and viruses.
(ii)Clear, colourless and transparent, with no suspended impurities.
(iii)Odourless and pleasant in taste.
(iv)Contains dissolved minerals and salts in suitable amounts, making it safe and healthy for drinking.

Que-4: What are the three methods of removing germs from natural water? Explain.

Ans- Natural water obtained from rivers, lakes, ponds, and wells may contain harmful microorganisms such as bacteria, viruses, and other disease-causing germs. These germs can spread diseases like cholera, typhoid, and dysentery. Therefore, water must be treated before it is used for drinking. The three main methods of removing germs from natural water are:

(i) Boiling : Boiling is the simplest and most effective household method of purifying water. Water is heated until it boils and is kept boiling for about 10–15 minutes. The high temperature kills harmful microorganisms present in the water. After boiling, the water is allowed to cool and is stored in clean containers.

(ii) Chlorination : In this method, chlorine or bleaching powder is added to water. Chlorine acts as a disinfectant and destroys disease-causing germs. This method is widely used in water treatment plants, swimming pools, and public water supplies because it is economical and effective for large quantities of water.

(iii) Distillation : Distillation is a process in which water is boiled to convert it into steam. The steam is then cooled and condensed back into liquid water. Harmful germs and dissolved impurities remain behind in the original container, while the condensed water obtained is pure and germ-free. This method is commonly used in laboratories to obtain chemically pure water.

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       Exercise IV on Water Class 6 Concise Chemistry ICSE Solutions

 Exercise IV on Water

Exercise IV

Objective Type Questions

Que-1: Water pollution is caused due to the addition of:
(i)domestic sewage
(ii)pesticides
(iii)effluents
(iv)all of the above

Ans- all of the above
Reason- Water pollution is caused by the addition of domestic sewage, pesticides, and industrial effluents into water bodies. These substances contaminate water, make it unsafe for drinking, harm aquatic life, and disturb the natural balance of aquatic ecosystems. Therefore, all of the above cause water pollution.

Que-2: One of the methods to control water pollution is:
(i)using synthetic detergents
(ii)passing wastewater through effluent and sewage treatment plants
(iii)washing clothes and utensils near water bodies
(iv)using more fertilizers, pesticides, etc.

Ans- passing wastewater through effluent and sewage treatment plants
Reason- Effluent and sewage treatment plants remove harmful pollutants, chemicals, and germs from wastewater before it is released into rivers, lakes, or other water bodies. This helps prevent water pollution and protects aquatic life and human health. The other options increase water pollution rather than control it.

Que-3: Excess rainfall may cause:
(i)floods
(ii)droughts
(iii)soil erosion
(iv)both (i) and (iii)

Ans- both (i) and (iii)
Reason- Excess rainfall can cause floods due to the overflow of rivers and water bodies. It can also lead to soil erosion, as the flowing water washes away the fertile top layer of soil. Therefore, both floods and soil erosion may result from excessive rainfall.

Que-4: Conservation of water can be done by :
(i)rainwater harvesting
(ii)planting trees and plants
(iii)avoiding misuse of water
(iv)all of the above

Ans- all of the above
Reason- Water can be conserved by rainwater harvesting, which collects and stores rainwater for future use; by planting trees and plants, which help increase groundwater recharge and reduce soil erosion; and by avoiding misuse of water, which prevents wastage. Therefore, all these methods help in the conservation of water.

Assertion Reason Type Questions

Que-1: Assertion: The sea water is saline.
Reason: The sea water contains many dissolved salts and minerals.
(i)Both A and R are true and R is the correct explanation of A.
(ii)Both A and R are true and R is not the correct explanation of A.
(iii)A is true and R is false.
(iv)A is false and R is true.

Ans- Both A and R are true and R is the correct explanation of A.
Reason — A is true as sea water is salty.
R is true as sea water contains many dissolved salts and minerals.

Que-2: Assertion: Water is a universal solvent.
Reason: Water has the ability to dissolve most of the solid, liquid and gaseous substances in it.
(i)Both A and R are true and R is the correct explanation of A.
(ii)Both A and R are true and R is not the correct explanation of A.
(iii)A is true and R is false.
(iv)A is false and R is true.

Ans- Both A and R are true and R is the correct explanation of A.
Reason — A is true as water is called a universal solvent.
R is true as water can dissolve a large number of substances.

Que-3: Assertion: Water is a mixture.
Reason: Water is made up of hydrogen and oxygen combined together in a 2 : 1 ratio by volume.
(i)Both A and R are true and R is the correct explanation of A.
(ii)Both A and R are true and R is not the correct explanation of A.
(iii)A is true and R is false.
(iv)A is false and R is true.

Ans- A is false and R is true.
Reason — A is false as water is not a mixture; it is a compound.
R is true as water is made of hydrogen and oxygen combined in a fixed ratio (2:1 by volume), which is a property of compounds.

Que-4: Assertion: Seeds need water to germinate and grow into plants.
Reason: Ice, liquid water and steam have different physical and chemical properties.
(i)Both A and R are true and R is the correct explanation of A.
(ii)Both A and R are true and R is not the correct explanation of A.
(iii)A is true and R is false.
(iv)A is false and R is true.

Ans- Both A and R are true and R is not the correct explanation of A.
Reason — A is true as seeds need water for germination because water activates enzymes and helps in growth.
R is true as ice, liquid water, and steam have different physical properties

Fill in the Blanks

Que-1: Water is a ….. ……. … solvent.

Ans- Water is a universal solvent.

Que-2: …. …. ……. is the purest form of natural water.

Ans- Rain water is the purest form of natural water.

Que-3: Sand and dust are ….. …. …… impurities in water.

Ans- Sand and dust are insoluble impurities in water.

Que-4: Sea water has a high concentration of ….. …… ….

Ans- Sea water has a high concentration of dissolved salts.

Que-5: Water covers nearly … ……… .. of the surface of the earth.

Ans- Water covers nearly 70 % of the surface of the earth.

Que-6: Evaporation of rain water leaves … ……… … residue.

Ans- Evaporation of rain water leaves no residue.

Que-7: …… …. ….. is the chemical added to water to remove the tiny suspended particles.

Ans- Alum is the chemical added to water to remove the tiny suspended particles.

Que-8: A … …….. …. is a uniform mixture of a solute and a solvent.

Ans- A solution is a uniform mixture of a solute and a solvent.

Que-9: Ice, water and steam have different physical states but are chemically …. ….. ……

Ans- Ice, water and steam have different physical states but are chemically identical.

Que-10: Boiling kills most of the …. …….. … in water.

Ans- Boiling kills most of the germs in water

Que-11: The elements present in the molecules of water are …. …. ……. and …. …… …..

Ans- The elements present in the molecules of water are hydrogen and oxygen.

State True or False

Write true or false for the following statements:

Que-1: Water is an element. ……………

Ans- False
Correct Statement — Water is a compound. Hydrogen and Oxygen are present in a fixed proportion in a water molecule.

Ans- True

Que-3: Tap water does not contain dissolved impurities. ……………

Ans- False
Correct Statement — Tap water usually contains some dissolved salts, minerals, and chlorine.

Que-4: Distillation is a good method for purifying water for town supply. ……………

Ans- False
Correct Statement — Distillation is good method to get water for medicinal purposes and in laboratories.

Match the Following

Ans- (a) – (2)
(b) – (3)
(c) – (1)

Short Answer Questions

Que-1: Name two water-borne diseases.

Ans- Two water-borne diseases are:
(i)Typhoid
(ii)Cholera

Que-2: What are effluents?

Ans- Effluents are liquid wastes or sewage discharged from homes, factories, industries, or treatment plants into rivers, lakes, seas, or other water bodies.

Que-3:`What is rainwater harvesting?

Ans- Rainwater harvesting is the process of collecting and storing rainwater from rooftops or other surfaces for future use.

Que-4:`What causes
(i) floods
(ii) soil erosion
(iii) droughts?

Ans- (i) Floods: Caused by excessive rainfall, overflowing rivers, or rapid melting of snow.
(ii) Soil erosion: Caused by the running action of water and wind, especially when there is little vegetation cover.
(iii) Droughts: Caused by very low rainfall or prolonged absence of rain over a long period.

Long Answer Questions

Que-1: What are the three main causes of water pollution ?

Ans- The three main causes of water pollution are:

(i) Domestic Sewage: Domestic sewage includes wastewater from homes, containing human excreta, soaps, detergents, food wastes, and other household wastes. When untreated sewage is discharged into rivers, lakes, and ponds, it contaminates the water and spreads water-borne diseases such as cholera and typhoid.
(ii) Industrial Effluents: Industries release liquid wastes called effluents, which may contain harmful chemicals, acids, dyes, oils, and heavy metals. When these untreated effluents are discharged into water bodies, they make the water toxic and harmful for aquatic life as well as human use.
(iii) Agricultural Runoff: Farmers often use fertilizers, pesticides, and insecticides to increase crop production. During rains, these chemicals are washed into nearby rivers, lakes, and ponds. This pollutes the water and affects aquatic plants and animals.

Que-2: State four steps to be taken to prevent water pollution.

Ans- The following four steps can be taken to prevent water pollution:

(i)Treat sewage before disposal: Domestic sewage should be properly treated in sewage treatment plants before being released into rivers, lakes, or other water bodies.
(ii)Treat industrial effluents: Industries should pass their liquid wastes through effluent treatment plants to remove harmful chemicals before discharge.
(iii)Reduce the use of fertilizers and pesticides: Excessive use of chemical fertilizers, insecticides, and pesticides should be avoided, as they can be washed into water bodies and cause pollution.
(iv)Do not dump waste into water bodies: Garbage, plastics, dead animals, and other wastes should not be thrown into rivers, lakes, ponds, or seas.

Que-3: (i) State three reasons to conserve water.
(ii) State four ways in which you as an individual can conserve water.

Ans- (i) Three Reasons to Conserve Water
(a)Fresh water is limited and only a small amount of the Earth’s water is available for human use.
(b)Water is essential for life, agriculture, industries, and domestic activities.
(c)Conserving water helps prevent water scarcity and ensures its availability for future generations.

(ii) Four Ways in Which an Individual Can Conserve Water
(a)Turn off taps when water is not in use, such as while brushing teeth.
(b)Repair leaking taps and pipes to prevent wastage of water.
(c)Use water carefully and avoid unnecessary wastage during bathing, washing, and cleaning.
(d)Practice rainwater harvesting by collecting and storing rainwater for future use.

Case Study Type Questions

Que-1: Siya kept two healthy potted plants A and B in sunlight. She watered plant A with tap water and plant B with saline water for a few days regularly. She observed that one of the plants grew well, the other could not.

(i) Which potted plant did not grow well ? Why ?
(ii) What is saline water ?
(iii) What conclusion can you draw from Siya’s experiment ?

Ans- (i) Plant B did not grow well because it was watered with saline water, which contains excess salts. High salt concentration makes it difficult for roots to absorb water (due to osmosis), leading to poor growth or even damage to the plant.
(ii) Saline water is water that contains a high amount of dissolved salts.
(iii) Plants grow well with normal water, but excess salt in water is harmful to plants and affects their growth.

Que-2: During summer, Radha noticed that the ponds near her house became dry. But in the rainy season, those same ponds overflow with water. Curious, she asked her teacher why this happens. Her teacher explained that heat from the sun changes water from rivers, lakes and ponds into water vapour. Water vapour then rises up and forms clouds. When clouds become heavy, they release water back to the earth as rain. This natural process keeps water circulating on the earth.
(i) What is this continuous circulation of water called?
(ii) What is the process by which water vapour turns back into tiny droplets of water?
(iii) In which season is the evaporation of water the fastest?
(iv) Write two uses of water in your daily life, apart from drinking.

Ans-(i) The Water Cycle
(ii) Condensation
(iii) Summer season
(iv) Bathing and Washing clothes

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Exercise I on Water Class 6 Concise Chemistry ICSE Solutions

Exercise I on Water

Objective Type Questions

Que-1: The water content in human body is:
(i)70%
(ii)75%
(iii)80%
(iv)90%

Ans- 70%
Reason: About 70% of the human body is made up of water, which is essential for various body functions.

Que-2: The purest form of natural water is:
(i)sea water
(ii)river water
(iii)rain water
(iv)lake water

Ans- rain water
Reason — Rain water is the purest form of water, formed by the evaporation of water from water bodies on the earth’s surfaces, followed by condensation of its vapour. The only impurities present in rain water are dust and dissolved, non-poisonous gases of air.

Que-3: When the water vapour changes into tiny droplets of water near the ground, it is called:
(i)mist
(ii)dew
(iii)fog
(iv)frost

Ans- fog
Reason — Fog is formed when the water vapour changes into tiny droplets of water near the ground.

Que-4: Water is a:
(i)compound
(ii)element
(iii)mixture
(iv)none of the above

Ans- compound
Reason — Water is made up of hydrogen and oxygen chemically combined in a fixed ratio (H₂O).

Que-5: Which of the following is a source of underground water?
(i)Rivers
(ii)Lakes
(iii)Ponds
(iv)Springs

Ans- Springs
Reason: Springs are places where underground water naturally comes out to the Earth’s surface.

Que-6: Under normal conditions, water exists as a:
(i)solid
(ii)liquid
(iii)gas
(iv)all of the above

Ans- liquid
Reason: At ordinary temperature and pressure, water remains in the liquid state.

Que-7: The most suitable source of water for domestic and industrial uses is :
(i)sea water
(ii)river water
(iii)spring water
(iv)rain water

Ans- river water
Reason: It is usually cleaner and contains fewer impurities than surface water.

One word answer

Que-1: What are the three states of water?

Ans- The three states of water are :
(i) Solid – Ice
(ii) Liquid – Water
(iii) Gas – Water Vapour

Short Answer Questions

Que-1: Name:
(i) Two major sources of natural water
(ii) Two sources of surface water
(iii) Two underground sources of water.

Ans- (i) Two major sources of natural water:
(a)Rain
(b)Snow
(ii) Two sources of surface water:
(a)Rivers
(b)Lakes
(iii) Two underground sources of water:
(a)Wells
(b)Springs.

Que-2: List three major impurities present in river water.

Ans- Three major impurities present in river water are:
(i)Suspended soil and sand particles
(ii)Dissolved salts and minerals
(iii)Germs

Que-3: Answer the following questions in brief:
(i) In which form is water present in the atmosphere?
(ii) Which source of water contains the highest concentration of salt in it ?
(iii) What possible impurities does rain water contain?
(iv) What is water table?

Ans- (i)Water vapour
(ii)Sea water
(iii)Dust particles, smoke, and dissolved gases
(iv)The upper level of underground water is called the water table.

Que-4: Find the percentage of water in the following:
(i) Rice and wheat grains
(ii) Eggs
(iii) Tomatoes
(iv) Bread
(v) Watermelon

Ans- (i) Rice and wheat grains — 10%
(ii) Eggs — 74%
(iii) Tomatoes — 95%
(iv) Bread — 35%
(v) Watermelon — 92%

Long Answer Questions

Que-1: What is water cycle? State two important roles of water cycle in nature.

Ans-  The water cycle is the continuous circulation of water between the earth’s surface and the atmosphere through the processes of evaporation, condensation, and precipitation. Water from oceans, rivers, lakes, and plants evaporates into the atmosphere, condenses to form clouds, and then falls back to the earth as rain, snow, or hail.

Two Important Roles of the Water Cycle in Nature

1. Maintains the supply of fresh water:
The water cycle continuously replenishes rivers, lakes, ponds, and underground water sources, providing fresh water for plants, animals, and human beings.
2. Maintains the balance of water in nature:
It ensures that water is constantly recycled between the atmosphere, land, and water bodies, helping to maintain ecological balance and support life on Earth.

Que-2: Give reason:
(i)Rain water is considered the purest form of natural water.
(ii)Spring water is pure enough for drinking but unsuitable for laboratory use.
(iii)The taste of spring water differs at different places.
(iv)Ice, water and steam are considered to have the same chemical composition.

Ans- (i) Rain water is formed by the evaporation of water from oceans, rivers, and lakes. During evaporation, dissolved salts and other impurities are left behind. Therefore, rain water is the purest natural form of water.
(ii) Spring water contains dissolved minerals and salts. These are not harmful for drinking but can interfere with chemical experiments. Hence, it is unsuitable for laboratory use.
(iii) Spring water dissolves different kinds and amounts of minerals and salts from the rocks and soil through which it passes. Therefore, its taste varies from place to place.
(iv) Ice, water, and steam are three physical states of the same substance, water. All of them contain only H₂O molecules; only their physical state differs. Hence, they have the same chemical composition.

Que-3: How are the following formed ?
(i) fog
(ii) mist
(iii) dew
(iv) frost.

Ans- (i) Fog is formed when the water vapour present in the air cools and condenses into tiny water droplets near the surface of the Earth. These droplets remain suspended in the air, reducing visibility.
(ii) Mist is formed when warm, moist air cools and water vapour condenses into very fine droplets suspended in the air. It is thinner than fog and does not reduce visibility as much.
(iii) Dew is formed when the temperature of the ground and objects on it falls below the dew point at night. Water vapour in the air condenses on cool surfaces such as grass, leaves, and metal objects as tiny droplets of water.
(iv) Frost is formed when the temperature falls below 0°C. Water vapour in the air changes directly into tiny ice crystals on cold surfaces without first becoming liquid water. This process is called deposition.

— : End of Exercise I on Water Class 6 Concise Chemistry ICSE Solutions :–

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Self Evaluation on Arithmetic Progression ICSE Class 10 Maths OP Malhotra (2026-27)

Self Evaluation on Arithmetic Progression

Self Evaluation on Arithmetic Progression ICSE Class 10 Maths OP Malhotra (2026-27)

Very Short Answer Type Questions (VSA)

1. Determine if the sequence 65, 60, 55, 50, 45, … is arithmetic. If so, give the common difference.

Sol: Given sequence = 65, 60, 55, 50, 45, …

Common difference,
d = 60 − 65 = −5
55 − 60 = −5
50 − 55 = −5
45 − 50 = −5

Since the common difference is the same throughout, the given sequence is an Arithmetic Progression (A.P.).
∴Yes, the sequence is an A.P. and its common difference is −5.

2. Find the 15th term of the sequence 5, 7, 9, 11, …

Sol: Here, a = 5, d = 2, n = 15.

Using the formula,
a_n = a + (n − 1)d

a₁₅ = 5 + (15 − 1) × 2
= 5 + 28
= 33

∴The 15th term is 33.

3. Find the next three terms of the sequence −14, −8, −2, 4, …

Sol: Common difference,
d = −8 − (−14) = 6.

Next three terms are:
4 + 6 = 10
10 + 6 = 16
16 + 6 = 22

∴The next three terms are 10, 16, 22.

4. If the first three terms of an A.P. are b, c and 2b, then find the ratio of b and c.

Sol: Since the terms are in A.P.,
c − b = 2b − c

2c = 3b

Therefore,
b : c = 2 : 3

Ans: b : c = 2 : 3.

5. Determine if the sequence 3, 6, 12, 24, 48, … is geometric. If yes, find the common ratio and the 12th term.

Sol: Common ratio,
r = 6/3 = 2
12/6 = 2
24/12 = 2

Since the common ratio is constant, the sequence is a G.P.

Here, a = 3, r = 2.

a₁₂ = ar¹¹
= 3 × 2¹¹
= 3 × 2048
= 6144

∴ Yes, it is a G.P. The common ratio is 2 and the 12th term is 6144.

6. Find the 5th term of a geometric sequence whose 3rd term is 8 and 4th term is 12.

Sol: Common ratio,
r = 12/8 = 3/2.

5th term = 4th term × r
= 12 × 3/2
= 18

∴ The 5th term is 18.

7. Find the sum of the first 100 natural numbers.

Sol: Using the formula,
S = n(n + 1)/2

S = 100 × 101 / 2
= 5050

∴ The sum of the first 100 natural numbers is 5050.

8. Find the sum of first 8 multiples of 3.

Sol: The first 8 multiples of 3 are:
3, 6, 9, 12, 15, 18, 21, 24.

Sum = 3 + 6 + 9 + 12 + 15 + 18 + 21 + 24
= 108

∴ The required sum is 108.

9. Find the sum of n terms of the series 4 − 8 + 16 − 32 + 64 + …

Sol: Here, a = 4, r = −2.

Using the formula,
S_n = a(rⁿ − 1)/(r − 1)

S_n = 4[(-2)ⁿ − 1]/(-2 − 1)
= 4[1 − (-2)ⁿ]/3

∴ S_n = 4[1 − (−2)ⁿ]/3.

10. Find the sum to n terms of the series 1 − 3x + 9x² − 27x³ + …

Sol: Here, a = 1, r = −3x.

Using the formula,
S_n = a(rⁿ − 1)/(r − 1)

S_n = [(-3x)ⁿ − 1]/(-3x − 1)
= [1 − (−3x)ⁿ]/(1 + 3x)

∴ S_n = [1 − (−3x)ⁿ]/(1 + 3x).

Multiple Choice Questions (MCQs)

1. The 50th term of the series 5, 9, 13, 17, … is

Sol: Here, a = 5, d = 4, n = 50.

Using the formula,
a_n = a + (n − 1)d

a₅₀ = 5 + (50 − 1) × 4
= 5 + 196
= 201

Ans: (c) 201.

2. The 7th term of the series 1, 3, 9, 27, 81, … is

Sol: This is a G.P. with
a = 1, r = 3, n = 7.

Using the formula,
a_n = arⁿ⁻¹

a₇ = 1 × 3⁶
= 729

Ans: (d) 729.

3. Determine k so that k + 2, 4k − 6 and 3k − 2 are three consecutive terms of an A.P.

Sol: Since the terms are in A.P.,
2(4k − 6) = (k + 2) + (3k − 2)

8k − 12 = 4k

4k = 12

k = 3

Ans: (b) 3.

4. 19th term of the series −87, −78, −69, −60, −51, … is

Sol: Here,
a = −87, d = 9, n = 19.

Using the formula,
a₁₉ = a + (n − 1)d

a₁₉ = −87 + (19 − 1) × 9
= −87 + 162
= 75

Ans: (b) 75.

5. In an A.P. if S₂₁ = 1250, S₂₀ = 1200, find a₂₁.

Sol: The 21st term is given by,

a₂₁ = S₂₁ − S₂₀
= 1250 − 1200
= 50

Ans: (d) 50.

6. Find the sum of first 25 terms of an A.P. whose nth term is 1 − 4n.

Sol: Given,
a_n = 1 − 4n

First term,
a = 1 − 4(1) = −3

Common difference,
d = −4

Using the formula,
S_n = n/2 [2a + (n − 1)d]

S₂₅ = 25/2 [2(−3) + 24(−4)]
= 25/2 (−6 − 96)
= 25/2 (−102)
= −1275

Ans: (a) −1275.

7. Which term of the series 1/4, −1/2, 1, … is 128?

Sol: The given series is a G.P. with
a = 1/4, r = −2.

Using the formula,
a_n = arⁿ⁻¹

1/4 × (−2)ⁿ⁻¹ = 128
(−2)ⁿ⁻¹ = 512 = 2⁹

Therefore,
n − 1 = 9
n = 10

Ans: (b) 10th.

8. If 1, x, y, z, 16 are in A.P., then what is the value of x + y + z?

Sol: Here,
a = 1, l = 16, n = 5.

Common difference,
d = (16 − 1)/(5 − 1)
= 15/4

Hence,
x = 1 + 15/4 = 19/4
y = 1 + 30/4 = 17/2
z = 1 + 45/4 = 49/4

Therefore,
x + y + z = 19/4 + 17/2 + 49/4
= 102/4
= 51/2

Ans: The correct value is 51/2.
Note: None of the given options is correct. There appears to be a misprint in the question.

9. How many terms of the geometric series 1 + 4 + 16 + 64 + … will make the sum 5461?

Sol: Here,
a = 1, r = 4.

Using the formula,
S_n = (4ⁿ − 1)/3

Given,
(4ⁿ − 1)/3 = 5461
4ⁿ − 1 = 16383
4ⁿ = 16384 = 4⁷

Therefore,
n = 7

Ans: (b) 7.

10. In a G.P., the sum of the first n terms is 364, the first term is 1 and the common ratio is 3. The value of n is

Sol: Here,
a = 1, r = 3.

Using the formula,
S_n = (3ⁿ − 1)/2

Given,
(3ⁿ − 1)/2 = 364
3ⁿ − 1 = 728
3ⁿ = 729 = 3⁶

Therefore,
n = 6

Ans: (c) 6.

11. If the fifth term of a G.P. is 2, then the product of its 9 terms is

Sol: In a G.P. having an odd number of terms, the product of all the terms equals the middle term raised to the number of terms.

Middle (5th) term = 2.

Therefore,
Product = 2⁹
= 512

Ans: (b) 512.

12. In a G.P., the ratio of the sum of the first 3 terms to that of the first 6 terms is 125 : 152. Find the common ratio of the G.P.

Sol: Using the sum formula of a G.P.,

(r³ − 1)/(r⁶ − 1) = 125/152

Since,
r⁶ − 1 = (r³ − 1)(r³ + 1),
1/(r³ + 1) = 125/152
r³ + 1 = 152/125
r³ = 27/125
r = 3/5

Ans: (d) 3/5.

— : End of Self Evaluation on Arithmetic Progression ICSE Class 10 Maths OP Malhotra (2026-27) :–

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Exercise I on Air Atmosphere

Exercise I on Air Atmosphere

Objective Type Questions

Que-1: Air consists of:
(i) only oxygen
(ii) only nitrogen
(iii) only carbon dioxide
(iv) all of these.

Ans- all of these.
Reason — The main gases present in air are nitrogen and oxygen. Besides these two gases, air also contains small quantities of carbon dioxide, water vapour, dust particles, smoke and traces of inert gases like helium, neon, argon, etc.

Que-2: The most abundant gas in Earth’s atmosphere is:
(i) oxygen
(ii) nitrogen
(iii) carbon dioxide
(iv) argon

Ans- nitrogen
Reason — The most abundant gas in Earth’s atmosphere is Nitrogen. The amount of nitrogen in air is 78%.

Que-3: Which of the following gases supports burning?
(i) oxygen
(ii) nitrogen
(iii) carbon dioxide
(iv) water vapour

Ans- oxygen
Reason — The ‘active part’ of air, which is used up when substances burn, is called oxygen. It is present about one-fifth of the total volume of the air.

Que-4: Air is a mixture because:
(i) the components of air retain their individual properties.
(ii) energy change takes place when the components of air are mixed together.
(iii) the composition of air remains the same everywhere.
(iv) the components of air cannot be separated by simple physical methods.

Ans- the components of air retain their individual properties.
Reason — Air is a mixture because the components of air retain their individual properties. Other options are not true because no energy change takes place, the composition of air varies from place to place and the components of air can be separated by physical methods.

Que-5: Oxygen in air is:
(i) 4/5 parts
(ii) 1/5 parts
(iii) 1/3 parts
(iv) negligible

Ans- 1/5 parts
Reason — The ‘active part’ of air i.e., oxygen is present about one-fifth (1/5 parts) of the total volume of the air.

Name the Following

Write the chemical name of:
(i) Lime Water
(ii) The White insoluble solid formed on reaction of carbon dioxide with lime water.

Ans- (i) Calcium hydroxide
(ii) Calcium carbonate

Long Answer Type Questions

Que-1: Why is air called a mixture ? Give five facts in support of your answer.

Ans- Air is called a mixture because it consists of several gases and other substances physically mixed together, not chemically combined.

Five facts in support of this statement:
(i) Air is made up of different gases: Air contains mainly nitrogen, oxygen, carbon dioxide, water vapour, argon and other gases.
(ii) The constituents of air retain their individual properties: Oxygen in air supports burning, carbon dioxide turns lime water milky, and nitrogen remains largely inactive. Each gas behaves as it would when separate.
(iii) The composition of air is not fixed: The amount of water vapour, carbon dioxide and dust particles varies from place to place and from time to time.
(iv) The components of air can be separated by physical methods: The gases present in air can be separated by processes such as fractional distillation of liquid air.
(v) No new substance is formed when the gases mix: The gases in air are only mixed together physically; they do not chemically combine to form a new substance.

Que-2: What are the main components of air ? Write down the composition of the three main gases present in air by volume.

Ans- Air is a mixture of several gases along with water vapour, dust particles and smoke. It forms the atmosphere that surrounds the Earth and is essential for the survival of living organisms. The major constituents of air are nitrogen, oxygen and carbon dioxide. Besides these, air also contains small amounts of argon, neon, helium, krypton and water vapour.

The composition of the three main gases present in air by volume is as follows:
(i) Nitrogen (N₂) – about 78%
(ii) Oxygen (O₂) – about 21%
(iii) Carbon dioxide (CO₂) – about 0.03–0.04%
The remaining about 1% consists of argon, water vapour and other rare gases.

Importance of the main gases:
(i) Nitrogen is required by plants for the manufacture of proteins and helps in maintaining soil fertility.
(ii) Oxygen is essential for respiration in living organisms and supports combustion.
(iii) Carbon dioxide is used by green plants during photosynthesis to prepare food and release oxygen.

— : End of Exercise I on Air Atmosphere Class 6 Concise Chemistry ICSE Solutions :–

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Exercise III on Air Atmosphere

Exercise III on Air Atmosphere

Objective Type Questions

Que-1: Air pollution is caused due to :
(i) cutting of green plants
(ii) smoke given out by factories
(iii) gases like carbon monoxide, sulphur dioxide, etc.
(iv) all of the above.

Ans- all of the above
Reason — Air pollution is the presence of harmful substances in the air that can affect human health, animals, plants, and the environment. It is caused by cutting green plants, smoke given out by factories and harmful gases like carbon monoxide and sulphur dioxide.

Que-2: The gases which cause acid rain are:
(i) sulphur dioxide and oxygen
(ii) nitrogen and oxygen
(iii) carbon dioxide and water vapour
(iv) nitrogen dioxide and sulphur dioxide.

Ans- nitrogen dioxide and sulphur dioxide
Reason — Gases like sulphur dioxide and nitrogen dioxide (pollutant) get mixed in rain water to form acid rain.

Que-3: Which of the following is not a greenhouse gas?
(i) Carbon dioxide
(ii) Sulphur dioxide
(iii) Methane
(iv) Nitrous oxide

Ans- Sulphur dioxide
Reason — Green house gases are carbon dioxide, methane, nitrous oxide, which traps more heat from the sunlight. In contrast, sulphur dioxide is not a green house gas.

Que-4: Common air pollutants that cause respiratory diseases are:
(i) ozone
(ii) inert gases
(iii) dust and smoke
(iv) water vapour

Ans- dust and smoke
Reason — Common air pollutants like dust and smoke cause respiratory, skin and eye problems.

Que-5: The gas responsible for ozone depletion is:
(i) oxygen
(ii) chlorofluorocarbons
(iii) carbon dioxide
(iv) sulphur dioxide

Ans- chlorofluorocarbons
Reason — Air pollutants like chlorofluorocarbons (CFCs) reacts with the ozone in the atmosphere and reduce the density of ozone in the stratosphere.

Fill in the Blanks

Que-1: The layer of air around the earth is called the .. …. ….. .

Ans- The layer of air around the earth is called the atmosphere.

Que-2: Although we cannot see air, we can …. … …. it.

Ans- Although we cannot see air, we can feel it.

Que-3: Air is a … …. …. of gases.

Ans- Air is a mixture of gases.

Que-4: Plants and animals maintain the balance of …. …. … and … …. …. in air.

Ans- Plants and animals maintain the balance of oxygen and carbon dioxide in air.

Que-5: Polluted air is …. … …. for health.

Ans- Polluted air is harmful for health.

Que-6: The supporter of combustion in air is …. … …. .

Ans- The supporter of combustion in air is oxygen.

Que-7: Green plants need .. ….. …. to prepare food.

Ans- Green plants need carbon dioxide to prepare food.

Que-8: Oxygen is used in …. … …. of the food to get …. .. ….. .

Ans- Oxygen is used in digestion of the food to get energy.

Que-9: Aquatic plants and animals use … ….. … in water.

Ans- Aquatic plants and animals use dissolved oxygen in water.

Que-10: The reddish brown powder on the surface of iron nails exposed to air and moisture is called … …… .. .

Ans- The reddish brown powder on the surface of iron nails exposed to air and moisture is called rust.

Ans- (a) – (ii)
(b) – (iv)
(c) – (v)
(d) – (iii)
(e) – (i)

Short Answer Questions

Long Answer Type Questions

Que-1: What is meant by ozone depletion?

Ans- Ozone depletion is the gradual thinning or reduction in the amount of the ozone layer present in the upper atmosphere (stratosphere). The ozone layer contains ozone gas (O₃), which acts as a protective shield by absorbing most of the harmful ultraviolet (UV) rays coming from the Sun.

The main cause of ozone depletion is the release of chemicals such as chlorofluorocarbons (CFCs), halons, and other ozone-depleting substances from refrigerators, air conditioners, aerosol sprays, and industrial processes. When these chemicals reach the stratosphere, they break down under sunlight and release chlorine and bromine atoms. These atoms react with ozone molecules and destroy them.

Que-2: Mention five causes of air pollution.

Ans- Five Causes of Air Pollution
(i)Burning of fossil fuels such as coal, petrol, and diesel in vehicles, industries, and power plants.
(ii)Industrial emissions that release harmful gases and smoke into the atmosphere.
(iii)Burning of garbage, wood, and crop residues, which produces smoke and toxic gases.
(iv)Deforestation, which reduces the number of trees available to absorb carbon dioxide and other pollutants.
(v)Dust and particulate matter from construction activities, mining, and roads that contaminate the air.

Que-3: State four steps to be taken to control air pollution.

Ans- Air pollution can be controlled by taking the following steps:
(i)Plant more trees: Trees absorb carbon dioxide and other harmful gases from the air and release oxygen. They help keep the air clean and fresh.
(ii)Use public transport and cleaner fuels: Using buses, trains, carpooling, or cleaner fuels reduces the number of vehicles on the roads and decreases air pollution.
(iii)Avoid burning garbage and crop waste: Burning waste produces smoke and harmful gases. Proper disposal and recycling of waste help reduce air pollution.
(iv)Control industrial emissions: Factories should install filters and other pollution-control devices in their chimneys to prevent harmful gases and dust from entering the atmosphere.

Que-4: Study the diagram and name the processes A, B and C.

Ans- (i) A is Respiration — Respiration is a chemical process that takes place in all living beings. In this process, oxygen that we breathe in with air reacts with the digested food in our body. This results in the release of energy, carbon dioxide and water.
(ii) B is Photosynthesis — Photosynthesis is a process in which carbon dioxide is used by green plants to prepare their food. Oxygen is released during this process which is then used for respiration by both plants and animals.
(iii) C is Burning of fuels — Burning (Combustion) is a process in which a substance reacts chemically with oxygen and gets oxidised, with the release of energy in the form of heat and light.

Que-5: In an experiment done with a burning candle, the apparatus was set up as shown below. Initially, the candle burns but after sometime it gets extinguished.

Look at the diagram and answer the questions given below.
(i) Label A and B.
(ii) Why does the candle burn in (I) but gets extinguished in (II) ?
(iii) Why does the water level rise after sometime ?
(iv) What conclusion is drawn by the experiment show above ?

Ans- (i) In the given diagram A and B are:
A → Air
B → Inactive air

(ii) The candle burn in (I) because of the presence of ‘active air’ that contains oxygen, which is used by the candle to burn. The candle does not burn in case of (II), because the jar consist of ‘inactive air’, consist mainly nitrogen, which does not support burning.

(iii) When the candle is lit in the jar, it starts burning using the active air present in the jar, upto one-fifth part of the jar containing oxygen helps the candle to burn. After sometime the candle gets extinguished and the water level rises upto one-fifth part of the jar to compensate the loss of oxygen.
(iv) This proves that air contains both oxygen and nitrogen. It clearly explains that air is made up of an ‘active’ part and an ‘inactive’ part. The ‘active’ part of air, which is used up when substances burn, is about one-fifth of the total volume of the air. It is a gas called oxygen. The ‘inactive’ part, which does not support burning, consists mainly of a gas called nitrogen, constituting 4/5th of air by volume.

Case Study Type Questions

Que-1: Riya was travelling with her parents in a big city. She noticed that the sky looked hazy and the buildings far away were not clearly visible. Her mother explained that this happens because harmful gases and tiny particles like smoke, soot and dust get mixed with the air. These come mainly from vehicles, burning of fuels and factories. Breathing such polluted air can make people sick and also harm animals and plants.
(i) Define air pollution?
(ii) Why is the air in big cities often less clear than in small towns or villages?
(iii) Mention two common health problems that people may suffer from due to air pollution.
(vi) Suggest two ways in which we can reduce harmful substances mixing in the air.
(v) How are solar energy and electrical energy better than using fossil fuels?

Ans- (i) Air pollution is the mixing of harmful substances in the air that make the air unsafe for living beings.
(ii) The air in big cities is often less clear because there are more vehicles, industries, and burning of fuels. These release large amounts of smoke, soot, and harmful gases into the air, making it hazy compared to cleaner air in villages.
(iii) Two common health problems caused by air pollution are coughing and eye irritation.
(vi) Two ways in which we can reduce harmful substances mixing in the air:
(i) Growing more trees and plants. Trees clean the environment and also help in bringing more rains which make the atmosphere free from pollutants.
(ii) Industries should be located far away from residential areas.
(v) Solar energy and electrical energy are better than fossil fuels because they do not produce smoke or harmful gases. They are clean, renewable, and help reduce air pollution and protect the environment.

— : End of Exercise III on Air Atmosphere Class 6 Concise Chemistry ICSE Solutions :–

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Exercise II on Air Atmosphere

Exercise II on Air Atmosphere

Objective Type Questions

Que-1: Rust is:
(i) hydrated iron oxide
(ii) hydrated copper sulphate
(iii) anhydrous iron oxide
(iv) none of the above

Ans- hydrated iron oxide
Reason — The reddish brown powdery mass that gets coated on the surface of some iron object when kept in moist air for a few days is called as rust. It is chemically know as hydrated iron oxide (Fe₂O₃.xH₂O)

Que-2: Photosynthesis is a process in which plants:
(i) take in oxygen and give out carbon dioxide
(ii) take in carbon dioxide and give out oxygen
(iii) take in nitrogen and give out oxygen.
(iv) none of the above

Ans- take in carbon dioxide and give out oxygen
Reason — Photosynthesis is a process through which green plants prepare their food in presence of sunlight with the help of carbon dioxide and water. In this process carbon dioxide is consumed and oxygen is released.

Que-3: Fuels which do not leave any residue on burning are:

(i) coal and wood
(ii) coal and LPG
(iii) wood and CNG
(iv) LPG and CNG.

Ans- LPG and CNG.
Reason — LPG And CNG are modern day fuels which do not leaves any residue on burning.

Que-4: Respiration :

(i) is a slow process
(ii) is a natural and continuous process
(iii) takes place at body temperature
(iv) all of the above

Ans- all of the above
Reason — Respiration is slow, natural and continuous process, and takes place at body temperature.

Que-5: Which of the following is common in combustion and respiration ?

(i) oxygen
(ii) release of heat and light
(iii) natural process
(iv) nitrogen

Ans- oxygen
Reason — Oxygen present in air is required for respiration of all living organisms and without oxygen, burning cannot take place. Hence oxygen is common in combustion and respiration.

Que-6: Which of the gas present in air is required for the synthesis of proteins in plants ?

(i) Oxygen
(ii) Nitrogen
(iii) Ozone
(iv) Carbon dioxide

Ans- Nitrogen
Reason — Nitrogen is needed to prepare a vital nutrient ‘protein’.

Que-7: Which component of air controls the climatic conditions?
(i) Inert gases
(ii) Oxygen
(iii) Water vapour
(iv) Nitrogen

Ans- Water vapour
Reason — Water vapour present in the air provides moisture and helps in predicting climatic conditions of a particular area. Its amount varies from place to place from time to time.

Name the Following

Que-1: Name two important processes supported by oxygen present in air.

Ans- Two important processes supported by oxygen present in air are:
(i) Respiration
(ii) Combustion (Burning)

Que-2: Name the gas used in:
(i) weather balloons
(ii) traffic lights
(iii) electric bulbs

Ans- (i) Helium
(ii) Neon
(iii) Argon

Long Answer Questions

Que-1: Give reason:
(i) Aquatic animals and plants are able to survive in water.
(ii) A burning candle stops burning if covered with a glass tumbler.
(iii) Mountaineers and divers carry oxygen cylinders with them.
(iv) When water is heated, we see bubbles rising up.

Ans- (i) Aquatic animals and plants are able to survive in water because water contains dissolved oxygen, which they use for respiration.
(ii) A burning candle needs oxygen for combustion. When it is covered with a glass tumbler, the limited oxygen inside gets used up and no fresh air can enter, so the candle stops burning.
(iii) At high altitudes, the air contains less oxygen available for breathing. Divers underwater cannot obtain oxygen from the surrounding water directly. Therefore, both mountaineers and divers carry oxygen cylinders to supply oxygen for respiration.
(iv) Water contains dissolved air. On heating, the dissolved air escapes from the water in the form of bubbles, which rise to the surface.

Que-2: State two similarities and two differences between respiration and burning.

Ans- The similarities and differences between respiration and burning are given :

Que-3: Define rusting. What are the two necessary conditions for rusting of iron ? Give the chemical name of rust.

Ans- Rusting is the slow process by which iron reacts with oxygen and moisture present in the air to form a reddish-brown coating called rust.
Two necessary conditions for rusting of iron are:
(i) Presence of oxygen (air).
(ii) Presence of water or moisture.
Chemical name of rust:
The chemical name of rust is hydrated iron(III) oxide (Fe₂O₃·xH₂O).

Que-4: Name the processes which maintain the balance between oxygen and carbon dioxide in the air. How is it done?

Ans- The processes that maintain the balance between oxygen and carbon dioxide in the air are photosynthesis and respiration.

How is it done?
(i) Photosynthesis: Green plants take in carbon dioxide from the air and, in the presence of sunlight and chlorophyll, prepare food. During this process, oxygen is released into the atmosphere.
(ii) Respiration: Humans, animals, and plants use oxygen to break down food and release energy. During respiration, carbon dioxide is given out into the air.

Thus, photosynthesis removes carbon dioxide and adds oxygen, while respiration removes oxygen and adds carbon dioxide, maintaining a balance of these gases in the atmosphere.

Que-5: (i) Why is nitrogen important to all living beings?
(ii) What is nitrogen fixation?

Ans- (i) Nitrogen is important to all living beings because it is an essential component of proteins and nucleic acids (DNA and RNA), which are required for growth, repair, and proper functioning of the body.
(ii) Nitrogen fixation is the process by which free atmospheric nitrogen is converted into nitrogen compounds (such as nitrates and ammonia) that plants can absorb and use.This process is carried out by certain bacteria, lightning, and industrial methods.

— : End of Exercise II on Air Atmosphere Class 6 Concise Chemistry ICSE Solutions :–

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Exercise I on Pure Substances and Mixtures; Separation of Mixtures Class 6 Concise Chemistry ICSE Solutions

Exercise I on Pure Substances and Mixtures; Separation of Mixtures

Objective Type Questions

Que-1: A mixture of mustard oil and water forms:
(i) a compound
(ii) an alloy
(iii) a homogeneous mixture
(iv) a heterogeneous mixture

Ans- a heterogeneous mixture
Reason — Mustard oil and water are immiscible liquids, their mixtures are not uniformly distributed throughout, Hence, they form a heterogeneous mixture.

Que-2: A heterogeneous mixture is:
(i) made up of only one kind of atoms
(ii) made up of only one kind of molecules
(iii) made up of different kinds of atoms and molecules.
(iv) one that looks uniform.

Ans-made up of different kinds of atoms and molecules.
Reason — A heterogeneous mixture is made up of different kinds of atoms and molecules which do not mix uniformly.

Que-3: An example of a homogeneous mixture is :
(i) distilled water
(ii) tap water
(iii) sand and water
(iv) sawdust and water

Ans-tap water
Reason — Tap water is a homogeneous mixture because it has minerals and salts, which are evenly mixed and looks uniform throughout.

Que-4: Which among the following is a set containing only mixtures ?
(i) gold, common salt, water, alloy
(ii) alloy, ink, honey, ice-cream
(iii) alloy, mercury, air, sea water
(iv) milk, duralumin, brass, silver.

Ans– alloy, ink, honey, ice-cream
Reason — The set “alloy, ink, honey, ice-cream” has only mixtures, because:
(a) Alloy : Mixture of metals
(b) Ink : Mixture of dyes and solvents
(c) Honey : Mixture of sugar and water
(d) Ice-cream : Mixture of milk, sugar, flavors and air.

Que-5: Copper is not a part of the alloy :
(i) brass
(ii) bronze
(iii) steel
(iv) duralumin

Ans– steel
Reason — Brass, bronze and duralumin has copper as their component along with other metals. Whereas, steel has iron and carbon.

Que-6: Which of the following is not a mixture?
(i) Sugar solution
(ii) Tap water
(iii) Milk
(iv) Distilled water

Ans-Distilled water
Reason — Distilled water is a pure substance, consisting of only H₂O molecules without any dissolved salts, minerals.

Que-7: Which of the following is a mixture ?
(i) Sugar
(ii) Honey
(iii) Common salt
(iv) Iron sulphite

Ans-Honey
Reason— Honey is a mixture of water and sugar.

Que: Identify the mixtures and compounds from the following list:

Air, water, sugar, salt, milk, tea, alcohol, honey, soil, glucose.

Classify the Following

Select the Odd One

Select the odd one out from the following:

(i) Salt solution, sugar solution, water and alcohol, sand and water
(ii) Chalk and sand, water and petrol, iron and sulphur, salt and water
(iii) Gold, iron sulphite, milk, water

Short Answer Questions

Que-1: Give two examples for each of the following types of mixtures.
(i) solid-solid
(ii) solid-liquid
(iii) liquid-gas
(iv) gas-gas

Ans- (i) Solid–Solid Mixtures: Sand and salt, Iron filings and sulphur powder
(ii) Solid–Liquid Mixtures: Salt dissolved in water, Sugar dissolved in water
(iii) Liquid–Gas Mixtures: Carbon dioxide dissolved in soft drinks (soda water), Oxygen dissolved in water
(iv) Gas–Gas Mixtures: Air (mainly nitrogen and oxygen), Natural gas (mixture of methane and other gases)

Que-2: Name the components present in the following mixtures:
(i) Brass
(ii) Duralumin
(iii) Tap water
(iv) Bronze

Ans-(i) Brass — Copper and zinc.
(ii) Duralumin — Aluminium, copper, magnesium and manganese.
(iii) Tap water — Water, dissolved salts, dissolved gases, minerals
(iv) Bronze — Copper, Tin and Zinc.

Que-3: Define the following with an example for each:
(i) Pure substance
(ii) Impure substance
(iii) Alloy
(iv) Solution
(v) Heterogeneous mixture
(vi) Homogeneous mixture

Ans- (i) Pure Substance: A substance made up of only one kind of particle and having a fixed composition.
Example: Distilled water, gold (24 carat).

(ii) Impure Substance: A substance that contains two or more different kinds of particles mixed together.
Example: Air, seawater.

(iii) Alloy: A homogeneous mixture of two or more metals, or a metal and a non-metal.
Example: Brass (copper and zinc), bronze (copper and tin).

(iv) Solution: A homogeneous mixture in which one substance (solute) is dissolved in another (solvent).
Example: Salt solution, sugar solution.

(v) Heterogeneous Mixture: A mixture in which the components are not uniformly distributed and can be distinguished.
Example: Sand and water, oil and water.

(vi) Homogeneous Mixture: A mixture in which the components are uniformly distributed throughout and cannot be distinguished.
Example: Air, salt dissolved in water.

Que-4: Give one difference between pure substances and mixtures.

Ans- The difference between pure substances and mixture are given below:

Que-5: What do you observe when a magnet is brought near a mixture of iron and sulphur ?

Ans- When a magnet is brought near a mixture of iron and sulphur, the iron particles are attracted by the magnet and get separated from the mixture, while the sulphur particles remain unaffected.
Observation: Iron filings stick to the magnet, whereas sulphur powder does not.
This shows that iron and sulphur in the mixture retain their individual properties and can be separated by physical means.

Long Answer Questions

Que-1: Give reason:
(i) Why do sugar and water retain their individual properties in a sugar solution?
(ii) Why do petrol and water form a heterogeneous mixture ?
(iii) Why does sulphur dissolve when carbon disulphite is added to a mixture of iron and sulphur but not when it is added to iron sulphite ?

Ans- (i) Sugar and water retain their individual properties in a sugar solution because a sugar solution is a mixture, not a new substance. Sugar and water do not react chemically with each other; they only mix physically. Therefore, both sugar and water retain their individual properties.

(ii) Petrol and water form a heterogeneous mixture because petrol and water are immiscible liquids and do not mix uniformly with each other. They form two separate layers, so the composition is not the same throughout the mixture, making it a heterogeneous mixture.

(iii) In a mixture of iron and sulphur, sulphur retains its own properties and dissolves in carbon disulphite, while iron does not. However, in iron sulphite, iron and sulphur are chemically combined to form a new compound. Since sulphur no longer exists as a separate substance, it does not dissolve in carbon disulphite.

Que-2: (i) State: Four differences between compounds and mixtures.
(ii) State: Three differences between water and air.

Ans-(i) The differences between compound and mixtures are given :

(ii) The difference between water and air are given :

Que-3: (i) Define ‘mixture’.
(ii) List four characteristics of a mixture.

Ans-(i) A mixture is a substance formed by the physical combination of two or more elements or compounds in any proportion, without any chemical reaction taking place between them.
(ii) Four characteristics of a mixture:
(a) The components of a mixture retain their individual properties.
(b) The components are not chemically combined.
(c) The components can be separated by physical methods.
(d) The composition of a mixture is not fixed; the components can be present in any proportion.

— : End of Exercise I on Pure Substances and Mixtures; Separation of Mixtures Class 6 Concise Chemistry ICSE Solutions :–

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Exercise II on Pure Substances and Mixtures; Separation of Mixtures Class 6 Concise Chemistry ICSE Solutions

Exercise II on Pure Substances and Mixtures; Separation of Mixtures

Objective Type Questions

Que-1: The process of adding a chemical substance to help the suspended solid particles to deposit as sediment faster is called:
(i) loading
(ii) sedimentation
(iii) decantation
(iv) filtration

Ans- loading
Reason — The process of helping fine solid particles in a solid-liquid mixture to settle faster, by adding a special chemical, is called loading or coagulation.

Que-2: Salt is separated from sea water by:
(i) evaporation
(ii) sublimation
(iii) magnetic separation
(iv) filtration

Ans- evaporation
Reason — Salt from sea water is separated by evaporation. Sea water is collected in shallow beds and allowed to evaporate in the sun. When all the water is evaporated, salt is left behind.

Que-3: A gas dissolved in a liquid can be separated by:
(i) filtration
(ii) boiling
(iii) using magnet
(iv) sublimation

Ans- boiling
Reason — A mixture of gas in liquid can be separated by heating or boiling. Dissolved gas escapes from the liquid on heating or boiling.

Que-4: Camphor can be separated from a mixture of sand and camphor by :
(i) filtration
(ii) evaporation
(iii) sublimation
(iv) winnowing

Ans-sublimation
Reason — Camphor can be separated from a mixture of sand and camphor by sublimation. The camphor sublimes and escapes as vapour, while the sand is left behind.

Que-5: A separating funnel is used to separate :
(i) miscible liquids
(ii) sugar solution
(iii) chalk powder and water
(iv) immiscible liquids

Ans- immiscible liquids
Reason — A separating funnel is a laboratory tool used to separate immiscible liquids. The denser liquid settles at the bottom, and the lighter one floats on top. When we open the stopcock the bottom layer drains first, effectively separating the two.

State True or False

Write “true” or “false” for the following statements:

Que-1: A pure substance consists of only one kind of atom or molecule. … .. ……

Ans- True

Que-2: The components of a mixture are present in a fixed ratio. .. ….. ….

Ans- False
Correct Statement — A mixture has no fixed composition, i.e. it is formed by mixing two or more substances in any ratio without any chemical reaction.

Que-3: Common salt is separated from its solution in water by decantation. …. … ….

Ans- False
Correct Statement — Common salt is separated from its solution in water by evaporation

Que-4: Winnowing is a process to remove small stones from grains. .. ….. ….

Ans- False
Correct Statement — Winnowing removes lighter husk from heavier grains, whereas, small stones are removed by hand picking or sieving.

Que-5: Gold jewellery is a homogeneous mixture of metals. … ….. …

Ans- True

Que-6: Air can be separated from water by filtration. … ….. …

Ans- False
Correct Statement — Air can be separated from water by heating or boiling.

Que-7: Salt and air dissolved in water add taste to water. ….. … …

Ans- True

Que-8: Steel is an alloy of iron and aluminium. … ….. …

Ans- False
Correct Statement— Steel is an alloy of iron and carbon.

Match the following:

Ans- (a) – (iii)
(b) – (iv)
(c) – (v)
(d) – (i) 
(e) – (ii)

One Word Answer Type Questions

Give one word for the following:

Que-1: The solid which is left on the filter paper after filtration.

Ans- Residue

Que-2: The solid particles which separate out from the solution on slow evaporation.

Ans- Crystals

Que-3: The solid particles that settle at the bottom of the beaker in a heterogeneous mixture of a solid and a liquid.

Ans- Sediment

Que-4: The clear liquid which is poured out after sedimentation.

Ans- Supernatant liquid

Que-5: The technique used to separate the light particles from heavy particles using the flow of wind.

Ans- Winnowing

Name the process by which the components of the following mixtures can be separated.

Que-1: Powdered glass and sugar

Ans- Solvent extraction method and filtration

Que-2: Chalk powder and iron filings

Ans- Magnetic separation

Que-3: Chaff and grain

Ans- Winnowing

Que-4: Salt and water

Ans- Evaporation

Que-5: Wheat and sugar

Ans- Sieving

Que-6: Sand and camphor

Ans- Sublimation

Que-7: Sugar and water

Ans- Evaporation

Rearrange the Following

Rearrange the following to get meaningful words:
(all are methods to separate the components of mixtures).

Que-1: OIRATVOPEAN
Que-2: DNOITITLLIAS
Que-3: FTOLINTRAI
Que-4: SINIVEG

Ans- (1) EVAPORATION
(2) DISTILLATION
(3) FILTRATION
(4) SIEVING

Short Answer Questions

Que-1: Name:
(i) two substances which can sublime
(ii) two substances soluble in water
(iii) two substances insoluble in water
(iv) four substances that can be used as filters.

Ans- (i) Two substances which can sublime:
(a)Iodine
(b)Ammonium chloride

(ii) Two substances soluble in water:
(a)Sugar
(b)Common salt

(iii) Two substances insoluble in water:
(a)Sand
(b)Chalk powder

(iv) Four substances that can be used as filters:
(a)Filter paper
(b)Cotton wool
(c)Muslin cloth
(d)Fine sieve (wire gauze)

Que-2: Give one example for each of the following types of mixtures.
(i) Solid-solid heterogeneous mixture
(ii) Solid-liquid heterogeneous mixture
(iii) Solid-liquid homogeneous mixture

Ans- (i) Solid-solid heterogeneous mixture: Mixture of iron filings and sulphur
(ii) Solid-liquid heterogeneous mixture: Sand and water
(iii) Solid-liquid homogeneous mixture: Sugar solution (sugar dissolved in water) or salt solution (salt dissolved in water)

Que-3: Define:
(i) Filtration
(ii) Sublimation
(iii) Evaporation
(iv) Sedimentation
(v) Decantation
(vi) Distillation

Ans-(i) Filtration: It is the process of separating an insoluble solid from a liquid by passing the mixture through a filter.

(ii) Sublimation: It is the process in which a solid changes directly into vapour on heating and the vapour changes back into solid on cooling, without passing through the liquid state.

(iii) Evaporation: It is the process by which a liquid changes into vapour from its surface at temperatures below its boiling point.

(iv) Sedimentation: It is the process in which heavier insoluble particles settle down at the bottom of a liquid when the mixture is left undisturbed.

(v) Decantation: It is the process of separating a liquid from settled insoluble solids by carefully pouring off the clear liquid without disturbing the sediment.

(vi) Distillation: It is the process of separating a soluble solid from a liquid or separating two liquids with different boiling points by heating the mixture and then condensing the vapour formed.

Long Answer Questions

Que-1: Why do we need pure substances ?

Ans- Pure substances are substances that contain only one kind of particle and have a fixed composition. We need pure substances for many important reasons:

(i) Accurate Scientific Experiments: Scientists require pure substances to obtain correct and reliable results. Impurities can affect observations and lead to incorrect conclusions.

(ii) Preparation of Medicines: Medicines must be pure to ensure their safety and effectiveness. Impurities may reduce the medicinal value or cause harmful side effects.

(iii) Industrial Processes: Many industries use pure substances to manufacture products of consistent quality. Impurities can affect the properties and performance of the final product.

(iv) Food Safety: Pure ingredients help maintain the quality, taste, and safety of food products. Contaminated substances may be harmful to health.
Study of Properties: The physical and chemical properties of a substance can be accurately determined only when it is pure.

Que-2: Give reason:
(i) Sand and sawdust cannot be separated by hand picking.
(ii) Magnet is used to separate a mixture of iron and sulphur.
(iii) Alum is used in purification of river water.

Ans- (i) Sand and sawdust cannot be separated by hand picking.
Hand picking is a method used to separate substances when the particles are large enough to be seen and picked out easily by hand. In a mixture of sand and sawdust, both substances are present as very small particles and are mixed closely together. Picking out each particle separately would be extremely difficult, time-consuming, and impractical. Therefore, sand and sawdust cannot be separated by hand picking. They can be separated by using water because sawdust floats on water while sand settles at the bottom.

(ii) Magnet is used to separate a mixture of iron and sulphur.
A magnet is used to separate a mixture of iron and sulphur because iron possesses magnetic properties whereas sulphur does not. When a magnet is brought near the mixture, the iron particles are attracted towards the magnet and can be removed easily, leaving behind the sulphur particles. Thus, the difference in magnetic properties of iron and sulphur makes magnetic separation possible.

(iii) Alum is used in purification of river water.
River water contains many fine suspended impurities such as clay, dust, and other insoluble particles. These particles are very light and do not settle down easily. Alum is added to the water because it causes these tiny suspended particles to stick together and form larger, heavier particles called flocs. These flocs settle at the bottom of the container, making the water clearer. The clear water can then be filtered and further treated for safe use. Therefore, alum is commonly used in the purification of river water.

Que-3: The following diagram shows a method employed for the separation of a mixture. Study the same and answer the following questions:

(i) Label the parts shown as A, B and C.
(ii) Write the name of the method depicted above.
(iii) What kind of mixture is separated by this method?
(iv) How can this process be made faster ?
(v) What is one disadvantage of this process ?

Ans- (i)  The parts shown as A, B, and C indicate the following:
A → Liquid
B → Evaporating dish
C → Bunsen burner
(ii) Evaporation is depicted in the given picture.
(iii) Homogeneous solid-liquid mixture is separated by this method.
(iv) Evaporation can be made faster by heating.
(v) In evaporation process, the solvent is lost to the environment in vapour form.

Case Study Type Questions

Que-1: Zainab was helping her mother in the kitchen. She took some rice grains in a bowl, which also contained a few small stones to sort. By mistake, she dropped a container of salt into the bowl, and salt got mixed with the rice grains. Her mother then asked her to separate the rice grains from the stones and the salt so that the rice would be clean and ready to cook for dinner later.
(i) What kind of mixture was formed by Zainab ?Justify your answer.
(ii) How will you separate the stones from the mixture? Name the method used.
(iii) What do you observe when water is added to the remaining mixture of rice grains and salt?
(vi) What will you do to separate rice grains from water?
(v) How will you recover the dissolved salt from the solution?

Ans- (i) The mixture formed is a heterogeneous mixture. Rice grains, small stones and salt are not uniformly mixed and can be seen separately before water is added.
(ii)Stones can be separated by handpicking. This method works because stones are visibly different in size, shape, and color from rice grains.
(iii) When water is added, the salt dissolves in water forming a salt solution, while the rice grains remain undissolved and settle down.
(vi) Rice can be separated from water by decantation (pouring off the water).
(v) The dissolved salt can be recovered by evaporation. When the solution is heated or left to evaporate, water evaporates and the salt remains behind as a solid.

— : End of Exercise II on Pure Substances and Mixtures; Separation of Mixtures Class 6 Concise Chemistry ICSE Solutions :–

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