Periodic Table Intex-1 Concise Class-10 ICSE Chemistry Selina Solutions Chapter-1. We Provide Step by Step Answer of Intex-1 Questions of Exercise-1 for ICSE Class-10. The given Solutions is according to the Latest editions. Visit official Website CISCE for detail information about ICSE Board Class-10.

Periodic Table Intex-1 Concise Class-10 ICSE Chemistry Selina Solutions Chapter-1

Board	ICSE
Book / Publication	Concise / Selina
Subject	Chemistry
Class	10th
Writer	Dr SP Singh
Chapter-1	Periodic Table (Periodic Properties and Variations of Properties)
Topics	Intex-1
Edition	2025-2026

Intex-1 Questions on Periodic Table

Page-5

Que-1: 

(i) State modern periodic law.
(ii) Name the scientist who stated the law.
(iii) How many groups and periods does modern periodic table have?

Ans:
(i) The modern periodic law states that “The properties of elements are the periodic functions of their atomic number.”
(ii) Henry Moseley put forward the modern periodic law.
(iii) Modern Periodic table has 7 periods and 18 groups.

Que-2: What are horizontal rows and vertical columns in a periodic table known as?

Ans: The horizontal rows are known as periods and vertical columns in the periodic table are known as groups.

Que-3: Periodicity is observed due to the similar………….(number of valence electrons/ atomic number/ electronic configuration)

Ans: Periodicity is observed due to the similar electronic configuration.

Que-4: How does electronic configuration in atoms change

(i) In a period from left to right?
(ii) In a group top to bottom?

Ans:
(i) Though the number of shells remain the same, number of valence electrons increases by one, as we move across any given period from left to right.
(ii) While going from top to bottom in a group, the number of shells increases successively i.e. one by one but the number of valence electrons remains the same.

Que-5: Name 2 elements in each case:

(i) Alkali metals
(ii) Alkaline earth metals
(iii) Halogens
(iv) Inert gas

Ans:
(i) Sodium and Potassium
(ii) Calcium and Magnesium
(iii) Chlorine and Bromine
(iv) Neon and Argon

Que-6: Elements of group 1 and elements of group 17 both have valency 1. Explain.

Ans: Valency is equal to the number of electrons an atom can donate or accept or share. Hence, it depends on the number of electrons in the outermost shell (i.e. valence shell).

Group 1 (IA) elements have one electron in their outermost shell. So they donate this one electron to become stable hence their valency is one. On the other hand, Group 17 (VIIA) elements have seven electrons in their outermost shell. So they accept one electron to attain stable electronic configuration hence their valency is also one.

Que-7: Correct the statements.

(i) Elements in the same period have equal valency.
(ii) Valency depends upon the number of shells in an atom.
(iii) Copper and zinc are representative elements.
(iv) Transition elements are placed at the extreme right of the periodic table.

Ans:
(i) Elements in the same group have equal valency.
(ii) Valency depends upon the number of valence electrons in an atom.
(iii) Copper and zinc are transition elements.
(iv) Noble gases are placed at the extreme right of the periodic table.

Que-8: What do you understand by?

(i) Periodicity
(ii) Typical elements
(iii) Orbits

Ans:
(i) The properties that reappear at regular intervals, or in which there is a gradual variation at regular intervals, are called periodic properties and the phenomenon is known as the periodicity of elements.
(ii) The third-period elements, Na, Mg, Al, Si, P and Cl summarize the properties of their respective groups and are called typical elements.
(iii) Elements revolve around the nucleus in certain definite circular paths called orbits or shells.

Que-9: Name 2 elements you would expect to show chemical reactions similar to calcium. What is the basis of your choice?

Ans: Beryllium and magnesium will show similar chemical reactions as calcium. Since these elements belong to same group 2 and also have two electrons in their outermost shell like calcium.

Que-10: Name the (i) metals, (ii) metalloids and (iii) non-metals in the first twenty elements.

Ans: (i) Metals: Lithium, Beryllium, Sodium, Magnesium, Aluminium, Potassium, Calcium
(ii) Metalloids: Boron, Silicon
(iii) Non-metals: Hydrogen, Helium, Carbon, Nitrogen, Oxygen, Fluorine, Neon, Phosphorous, Sulphur, Chlorine, Argon

Que-11: Fluorine, Chlorine and Bromine are put in one group on the basis of their similar properties.

(i)What are those similar properties?
(ii)What is the common name of this group or family?

Ans:
(i) Properties: Non-metallic, highest electronegativity in the respective periods, highest ionisation potentials in the respective periods, highest electron affinity in the respective periods
(ii) Salt-forming; hence, the common name is halogens.

Que-12: What is the main characteristic of the last element in each period of the Periodic Table? What is the general name of such elements?

Ans: The main characteristic of the last element in each period of the periodic table is they are inert or chemically un reactive. The general name of such elements is ‘Noble gases’.

Que-13: According to atomic structure, what determines which element will be the first and which will be the last in a period?

Ans: According to atomic structure, the number of valence electrons determines the first and the last element in a period.

Que-14: How do the following vary on moving from left to right in the third period of the periodic table :

(i) valence electrons and
(ii) valency

Ans:
(i) The number of valence electron successively increases by one as we move from left to right in the third period.
(ii) Valency firstly increase from 1 to 4 from element sodium (Na) to silicon (Si) and then reduces to zero from element phosphorus (P) till chlorine (Cl) as we move from left to right in the third period.

Que-15: Name the type of elements, which have their

(i) Outermost shell complete
(ii) Outermost shell incomplete
(iii) Two outermost shells incomplete
(iv) One electron short of octet
(v) Two electrons in the outermost orbit.

Ans:
(i) Noble gases
(ii) Representative elements
(iii) Transition elements
(iv) Halogens
(v) Alkaline Earth metals

Que-16: An element has 2 electrons in its N shell

(i) What is its atomic number?
(ii) State its position in periodic table
(iii) Is it metal or non-metal?
(iv) State the name assigned to this group.
(v) what is the valency of this elements.

Ans:
(i) 20
(ii) It belongs to group 2 and fourth period.
(iii) It is a metal.
(iv) The name assigned to this group is IIB.
(v) valency is +2

Que-17: Answer the following in respect of element ³²S₁₆.

(i)Give its electronic configuration.
(ii)To which group and period does it belong?
(iii)What is its valency?
(iv)Is it metal or non-metal?
(v) Is it a reducing agent or oxidizing agent?
(vi)Give its formula with Hydrogen .

Ans:
(i) Electronic configuration of S: 2,8,6
(ii) 16th Group and 3rd Period.
(iii) Valency of S = 8 – 6 = 2
(iv) Sulphur is a non-metal.
(v) It is an oxidizing agent.
(vi) Formula with Hydrogen = H₂S

Que-18: Name:

(a) An alkali metal in period 3 and halogen in period 2.
(b) The noble gas with 3 shells.
(c) The non-metals present in period 2 and metals in period 3.
(d) The element of period 3 with valency 4.
(e) The element in period 3 which does not form oxide.
(f) The element of lower nuclear charge out of Be and Mg.

Ans:
(a) Alkali metal in period 3 = Sodium
Halogen in period 2 = Fluorine
(b) Argon (Ar).
(c) Carbon (C), Nitrogen (N), Oxygen (O), Fluorine (F), Neon (Ne) are non-metals in period 2.
Sodium (Na), Magnesium (Mg) and Aluminium (Al)are metals in period 3.
(d) Silicon (Si).
(e) Argon (Ar).
(f) Be will have lower nuclear charge then Mg.

Que-19: The electronic configuration of an element T is 2, 8, 8, 1.

(i) What is the group number of T ?
(ii) What is the period number of T ?
(iii) How many valence electrons are there in an atom of T ?
(iv) What is the valency of T ?
(v) Is it a metal or a non-metal ?

Ans:
(i) Group Number of T is 1.
(ii) Period of T is 4.
(iii) Their is 1 valence electron present in atom T.
(iv) Valency of T is 1.
(v) It is a Metal.

Que-20: Match the atomic number 19, 15, 8, 4 and 2 with each of the following:

(i) A metal of valency one
(ii) A solid non-metal of period 3
(iii) A rare gas
(iv) A gaseous element with valency 2
(v) An element of group 2

Ans:
(i) A metal of valency one = 19
(ii) A solid non-metal of period 3 = 15
(iii) A rare gas = 2
(iv) A gaseous element with valency 2 = 8
(v) An element of group 2 = 4

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