Class 9 Science Ch 4–Structure of the Atoms Intext Questions and Answer | NCERT Solutions

Class 9 Science Chapter 4 Structure of the Atom ke Intext Questions and Answers yahan apko simple aur easy language me diye gaye hain. Ye NCERT solutions exam oriented hain students ko chapter ke concepts—electron, proton, neutron, atomic models aur isotopes—ko achhe se samajhne me help karte hain. Har intext question ka clear, accurate aur exam-oriented answer diya gaya hai jisse aap apni board exam preparation ko strong bana sakte hain.

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STRUCTURE OF THE ATOMS

INTEXT QUESTION-ANSWER

Intext Question - Page 39

Ques 1 :- What are canal rays ?

Ans :- Canal rays are positively charged radiations discovered by E. Goldstein in a discharge tube. These rays led to the discovery of proton.

-- These rays are called canal rays because these rays passed through the holes or canals in the cathode.

Ques 2:- If an atom contains one electron and one proton, will it carry any charge or not?

Ans :- No, it will not carry any charge. (The charge will cancel each other). 

Intext Question - Page  41

Ques 1 :- On the basis of Thomson’s model of an atom, explain how the atom is neutral as a whole.

Ans :- In 1899, Thomson proposed that :

(i) An atom consists of a positively charged sphere and the electrons are embedded in it.

(ii) The negative and positive charges balance each other and so the atom as a whole is neutral.

Ques 2 :- On the basis of Rutherford’s model of an atom, which subatomic particle is present in the nucleus of an atom?

Ans :- On the basis of Rutherford's model of an atom proton is present in the nucleus of an atom.

Ques 3 :- Draw a sketch of Bohr’s model of an atom with three shells.

Ans :-

Fig. :- Energy shells around the nucleus of an atom.

Ques 4: - What do you think would be the observation if the α-particle scattering experiment is carried out using a foil of a metal other than gold?

Ans :- Gold is the most malleable metal and hence increases the probability of the α-particle hitting the atom in the first plane. Also gold is the least reactive metal.

-- If any other metal is used other than gold, the metal may react with the α-particles or the α-particles may not be able to hit the atom if the metal is thick and less malleable.

Intext Question - Page  41

Ques 1 :- Name the three sub-atomic particles of an atom.

Ans :- The three sub-atomic particles of an atom are :-

-- electrons  (Negatively Charged),

-- protons (Positively Charged),

-- Neutrons (No Charge) .

Ques 2:- Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have ?

Ans :-  Atomic mass of Helium atom = 4u

Atomic mass = Number of Proton + Number of Neutrons

Number of Neutrons = Atomic mass - Number of Proton

Number of Neutrons = 4-2  = 2

Hence Helium has 2 neutrons.

 

Intext Question - Page  42

Ques 1 :- Write the distribution of electrons in carbon and sodium atoms.

 

Ans :- (i) Atomic number Of carbon = 6

Distribution Of electrons = 

K	L
2	4

(ii) Atomic number Of Sodium = 11

Distribution Of electrons =

K	L	M
2	8	1

Ques 2:- If K and L shells of an atom are full, then what would be the total number of electrons in the atom ?

 

Ans:- If  K and L shells of an atom are full then the total number of electrons in the atom would be 10.

(K shell can maximum 2 electrons and L shell can have maximum 8 electrons).

Intext Question - Page  44

Ques 1:- How will you find the valency of chlorine, Sulphur and magnesium ?

Ans:-

 

 

Intext Question - Page  44

Ques 1 :- If number of electrons in an atom is 8 and number of protons is also 8, then

(i) what is the atomic number of the atom? and

(ii) what is the charge on the atom?

 

Ans :- Atomic number = Number of protons = 8.

(ii) As number of protons (+ve charge) = number of electrons (-ve charge).

So, both the charges positive (+ve) and negative (-ve) neutralise each other.
Therefore, the atom does not possess any charge.

Ques 2 :- With the help of Table 4.1, find out the mass number of oxygen and Sulphur atom.

Ans :- Atomic mass number = No. of protons + No. of neutrons

Atomic mass number of oxygen = 8 + 8 = 16

Atomic mass number of Sulphur= 16 + 16 =32.

Intext Question - Page  45

Ques 1 :- For the symbol H,D and T tabulate three sub-atomic particles found in each of them.

Ans :-

Ques 2 :- Write the electronic configuration of any one pair of isotopes and isobars.

Ans :- (i) * Isotopes :- same atomic number but different mass numbers

Isotopes ¹²₆C and ¹⁴₆C

Electronic configuration	K	L
Carbon (C)	2	4

* Isobars :- same mass numbers but different atomic number.

(ii) Isobars ⁴⁰₁₈ Ar and ⁴⁰₂₀ C

Electronic configuration	K	L	M	N
Argon (Ar)	2	8	8
Calcium (Ca)	2	8	8	2

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In this chapter, we learned how different atomic models and discoveries helped us understand the internal structure of an atom. The Intext Questions and Answers of Class 9 Science Chapter 4 – Structure of the Atom provide clear explanations of important concepts such as electrons, protons, neutrons, isotopes, and isobars. These answers will help students strengthen their basic understanding and prepare well for exams. By revising these solutions regularly, learners can easily grasp the fundamental idea of how atoms form the basis of all matter around us.