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Class 9 · Science · Chapter 4: Structure of the Atom

BSEB Class 9 Science Chapter 4: Objective Questions (MCQ) with Answers

Bihar Board · NCERT · CBSE

All 78 objective questions (MCQ) of this chapter — solve first, then tap “Show answer”. Each question shows its source label: «BSEB 2025 · board paper» = verified from the official board paper; «Board-style (practice)» = Study With Me's own practice questions.

← Chapter 4: Structure of the Atom — full notes, video, questions

1Check1 mark

Who discovered canal rays?

  1. (A) J.J. Thomson
  2. (B) E. Goldstein
  3. (C) Chadwick
  4. (D) Bohr
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Correct answer: (B) E. Goldstein

E. Goldstein, in 1886.

2Check1 mark

In Thomson's model, the watermelon seeds stand for

  1. (A) protons
  2. (B) electrons
  3. (C) neutrons
  4. (D) the nucleus
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Correct answer: (B) electrons

Seeds = electrons.

3Check1 mark

In the scattering experiment, about one in how many α-particles rebounded?

  1. (A) 100
  2. (B) 1000
  3. (C) 12000
  4. (D) 10⁵
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Correct answer: (C) 12000

One in every 12000.

4Check1 mark

According to Rutherford, almost all the mass of an atom is in

  1. (A) the electrons
  2. (B) the nucleus
  3. (C) the empty space
  4. (D) the orbits
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Correct answer: (B) the nucleus

The nucleus.

5Check1 mark

According to Bohr, an electron in a discrete orbit

  1. (A) radiates energy
  2. (B) does not radiate energy
  3. (C) falls into the nucleus
  4. (D) becomes a proton
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Correct answer: (B) does not radiate energy

It does not radiate energy.

6Check1 mark

Who discovered the neutron?

  1. (A) Goldstein
  2. (B) Chadwick
  3. (C) Thomson
  4. (D) Rutherford
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Correct answer: (B) Chadwick

J. Chadwick, 1932.

7Check1 mark

The electronic configuration of sodium (Z = 11) is

  1. (A) 2, 8
  2. (B) 8, 2, 1
  3. (C) 2, 1, 8
  4. (D) 2, 8, 1
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Correct answer: (D) 2, 8, 1

2, 8, 1.

8Check1 mark

The valency of oxygen (2, 6) is

  1. (A) 6
  2. (B) 2
  3. (C) 8
  4. (D) 0
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Correct answer: (B) 2

8 − 6 = 2.

9Check1 mark

The mass number of aluminium (13 protons, 14 neutrons) is

  1. (A) 13
  2. (B) 14
  3. (C) 27
  4. (D) 1
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Correct answer: (C) 27

13 + 14 = 27.

10Check1 mark

An isotope of which element is used to treat goitre?

  1. (A) uranium
  2. (B) cobalt
  3. (C) iodine
  4. (D) carbon
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Correct answer: (C) iodine

Iodine.

11Check1 mark

What is the same in isobars?

  1. (A) atomic number
  2. (B) mass number
  3. (C) electrons
  4. (D) protons
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Correct answer: (B) mass number

Mass number.

12Book-based · Intro · p. 461 mark

According to Dalton, the atom is

  1. (A) indivisible and indestructible
  2. (B) charged
  3. (C) hollow
  4. (D) divisible
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Correct answer: (A) indivisible and indestructible

Answer: indivisible and indestructible.

13Book-based · Intro · p. 461 mark

Who identified the electron?

  1. (A) Niels Bohr
  2. (B) J.J. Thomson
  3. (C) E. Goldstein
  4. (D) J. Chadwick
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Correct answer: (B) J.J. Thomson

Answer: J.J. Thomson.

14Book-based · Intro · p. 461 mark

Canal rays were discovered in

  1. (A) 1932
  2. (B) 1856
  3. (C) 1886
  4. (D) 1906
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Correct answer: (C) 1886

Answer: 1886.

15Book-based · Intro · p. 461 mark

Canal rays are

  1. (A) neutral
  2. (B) sometimes positive, sometimes negative
  3. (C) negatively charged
  4. (D) positively charged
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Correct answer: (D) positively charged

Answer: positively charged.

16Book-based · Intro · p. 461 mark

Canal rays led to the discovery of the

  1. (A) proton
  2. (B) α-particle
  3. (C) electron
  4. (D) neutron
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Correct answer: (A) proton

Answer: proton.

17Book-based · 4.1 · p. 461 mark

The mass of a proton is about ___ that of an electron.

  1. (A) equal to
  2. (B) 2000 times
  3. (C) 12000 times
  4. (D) half
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Correct answer: (B) 2000 times

Answer: 2000 times.

18Book-based · 4.1 · p. 461 mark

The charge on an electron is

  1. (A) +1
  2. (B) 0
  3. (C) −1
  4. (D) +2
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Correct answer: (C) −1

Answer: −1.

19Book-based · 4.1 · p. 461 mark

A proton is represented as

  1. (A) n
  2. (B) α
  3. (C) e⁻
  4. (D) p⁺
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Correct answer: (D) p⁺

Answer: p⁺.

20Book-based · Activity 4.1 · p. 461 mark

In Activity 4.1 the glass rod is rubbed with

  1. (A) silk cloth
  2. (B) paper
  3. (C) plastic
  4. (D) woollen cloth
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Correct answer: (A) silk cloth

Answer: silk cloth.

21Book-based · Activity 4.1 · p. 461 mark

A comb run through dry hair attracts bits of paper because

  1. (A) the comb becomes a magnet
  2. (B) the comb becomes charged
  3. (C) the paper is wet
  4. (D) of air currents
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Correct answer: (B) the comb becomes charged

Answer: the comb becomes charged.

22Book-based · 4.2.1 · p. 461 mark

Who gave the first model of the atom?

  1. (A) Rutherford
  2. (B) Bohr
  3. (C) Thomson
  4. (D) Chadwick
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Correct answer: (C) Thomson

Answer: Thomson.

23Book-based · Fig. 4.1 · p. 471 mark

Thomson's model was compared to

  1. (A) a ladder
  2. (B) a barbed-wire fence
  3. (C) the solar system
  4. (D) a Christmas pudding / watermelon
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Correct answer: (D) a Christmas pudding / watermelon

Answer: a Christmas pudding / watermelon.

24Book-based · 4.2.1 · p. 471 mark

In Thomson's model the red pulp of the watermelon stands for

  1. (A) positive charge
  2. (B) neutrons
  3. (C) empty space
  4. (D) electrons
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Correct answer: (A) positive charge

Answer: positive charge.

25Book-based · 4.2.1 · p. 471 mark

According to Thomson the atom is neutral because

  1. (A) it has no electrons
  2. (B) positive and negative charges are equal
  3. (C) it has neutrons
  4. (D) the nucleus is neutral
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Correct answer: (B) positive and negative charges are equal

Answer: positive and negative charges are equal.

26Book-based · 4.2.1 · p. 471 mark

J.J. Thomson received the Nobel Prize in Physics in

  1. (A) 1922
  2. (B) 1932
  3. (C) 1906
  4. (D) 1908
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Correct answer: (C) 1906

Answer: 1906.

27Book-based · 4.2.1 · p. 471 mark

For how many years was Thomson director of the Cavendish Laboratory?

  1. (A) 50
  2. (B) 10
  3. (C) 20
  4. (D) 35
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Correct answer: (D) 35

Answer: 35.

28Book-based · 4.2.2 · p. 471 mark

Rutherford used a foil of

  1. (A) gold
  2. (B) copper
  3. (C) silver
  4. (D) aluminium
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Correct answer: (A) gold

Answer: gold.

29Book-based · 4.2.2 · p. 471 mark

The gold foil was about ___ thick.

  1. (A) 10 atoms
  2. (B) 1000 atoms
  3. (C) 12000 atoms
  4. (D) 1 mm
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Correct answer: (B) 1000 atoms

Answer: 1000 atoms.

30Book-based · 4.2.2 · p. 471 mark

α-particles are

  1. (A) hydrogen atoms
  2. (B) electrons
  3. (C) doubly-charged helium ions
  4. (D) neutrons
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Correct answer: (C) doubly-charged helium ions

Answer: doubly-charged helium ions.

31Book-based · 4.2.2 · p. 471 mark

The mass of an α-particle is

  1. (A) 12 u
  2. (B) 1 u
  3. (C) 2 u
  4. (D) 4 u
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Correct answer: (D) 4 u

Answer: 4 u.

32Book-based · 4.2.2 · p. 481 mark

In the scattering experiment most α-particles

  1. (A) passed straight through
  2. (B) got stuck in the foil
  3. (C) turned by 90°
  4. (D) rebounded
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Correct answer: (A) passed straight through

Answer: passed straight through.

33Book-based · 4.2.2 · p. 481 mark

Most α-particles passing straight through shows that

  1. (A) the nucleus is large
  2. (B) most of the atom is empty space
  3. (C) electrons are heavy
  4. (D) gold is transparent
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Correct answer: (B) most of the atom is empty space

Answer: most of the atom is empty space.

34Book-based · 4.2.2 · p. 481 mark

α-particles deflected by 180° show that

  1. (A) the atom is not hollow
  2. (B) neutrons exist
  3. (C) all the positive charge and mass are in a very small volume
  4. (D) electrons are in the nucleus
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Correct answer: (C) all the positive charge and mass are in a very small volume

Answer: all the positive charge and mass are in a very small volume.

35Book-based · 4.2.2 · p. 481 mark

The radius of the nucleus is about ___ times less than that of the atom.

  1. (A) 10¹⁰
  2. (B) 10
  3. (C) 10²
  4. (D) 10⁵
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Correct answer: (D) 10⁵

Answer: 10⁵.

36Book-based · 4.2.2 · p. 481 mark

"A 15-inch shell at tissue paper" described which observation?

  1. (A) rebounding
  2. (B) the foil melting
  3. (C) passing straight
  4. (D) small-angle deflection
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Correct answer: (A) rebounding

Answer: rebounding.

37Book-based · 4.2.2 · p. 481 mark

Who is known as the "Father of nuclear physics"?

  1. (A) Bohr
  2. (B) Rutherford
  3. (C) Thomson
  4. (D) Dalton
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Correct answer: (B) Rutherford

Answer: Rutherford.

38Book-based · 4.2.2 · p. 481 mark

Rutherford received the Nobel Prize in Chemistry in

  1. (A) 1932
  2. (B) 1906
  3. (C) 1908
  4. (D) 1922
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Correct answer: (C) 1908

Answer: 1908.

39Book-based · 4.2.2 · p. 481 mark

In Rutherford's model electrons

  1. (A) are embedded in a sphere
  2. (B) are bound to neutrons
  3. (C) are fixed in the nucleus
  4. (D) revolve around the nucleus in circular paths
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Correct answer: (D) revolve around the nucleus in circular paths

Answer: revolve around the nucleus in circular paths.

40Book-based · 4.2.2 · p. 481 mark

The main drawback of Rutherford's model:

  1. (A) it could not explain the stability of the atom
  2. (B) it ignored electrons
  3. (C) it gave no mass
  4. (D) it did not explain the nucleus
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Correct answer: (A) it could not explain the stability of the atom

Answer: it could not explain the stability of the atom.

41Book-based · 4.2.2 · p. 481 mark

An accelerating charged particle in a circular orbit

  1. (A) becomes neutral
  2. (B) radiates energy
  3. (C) absorbs energy
  4. (D) stops
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Correct answer: (B) radiates energy

Answer: radiates energy.

42Book-based · 4.2.3 · p. 491 mark

Who proposed discrete orbits?

  1. (A) Goldstein
  2. (B) Rutherford
  3. (C) Niels Bohr
  4. (D) Chadwick
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Correct answer: (C) Niels Bohr

Answer: Niels Bohr.

43Book-based · 4.2.3 · p. 491 mark

Bohr received the Nobel Prize in

  1. (A) 1932
  2. (B) 1908
  3. (C) 1916
  4. (D) 1922
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Correct answer: (D) 1922

Answer: 1922.

44Book-based · Fig. 4.3 · p. 491 mark

Shells are represented by the letters

  1. (A) K, L, M, N
  2. (B) P, Q, R, S
  3. (C) s, p, d, f
  4. (D) A, B, C, D
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Correct answer: (A) K, L, M, N

Answer: K, L, M, N.

45Book-based · Fig. 4.3 · p. 491 mark

For the M shell, n =

  1. (A) 2
  2. (B) 3
  3. (C) 4
  4. (D) 1
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Correct answer: (B) 3

Answer: 3.

46Book-based · 4.2.4 · p. 491 mark

The neutron was discovered in

  1. (A) 1906
  2. (B) 1922
  3. (C) 1932
  4. (D) 1886
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Correct answer: (C) 1932

Answer: 1932.

47Book-based · 4.2.4 · p. 491 mark

The charge on a neutron is

  1. (A) +2
  2. (B) +1
  3. (C) −1
  4. (D) 0
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Correct answer: (D) 0

Answer: 0.

48Book-based · 4.2.4 · p. 491 mark

Which atom has no neutron in its nucleus?

  1. (A) (ordinary) hydrogen
  2. (B) carbon
  3. (C) lithium
  4. (D) helium
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Correct answer: (A) (ordinary) hydrogen

Answer: (ordinary) hydrogen.

49Book-based · 4.2.4 · p. 491 mark

The mass of an atom is the sum of the masses of

  1. (A) electrons + protons
  2. (B) protons + neutrons
  3. (C) electrons + neutrons
  4. (D) electrons only
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Correct answer: (B) protons + neutrons

Answer: protons + neutrons.

50Book-based · 4.3 · p. 491 mark

The distribution of electrons in shells was suggested by

  1. (A) Dalton
  2. (B) Chadwick
  3. (C) Bohr and Bury
  4. (D) Thomson and Rutherford
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Correct answer: (C) Bohr and Bury

Answer: Bohr and Bury.

51Book-based · 4.3 · p. 491 mark

The maximum number of electrons in a shell is given by

  1. (A) 8n
  2. (B) n²
  3. (C) 2n
  4. (D) 2n²
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Correct answer: (D) 2n²

Answer: 2n².

52Book-based · 4.3 · p. 501 mark

Maximum electrons in the L shell:

  1. (A) 8
  2. (B) 18
  3. (C) 32
  4. (D) 2
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Correct answer: (A) 8

Answer: 8.

53Book-based · 4.3 · p. 501 mark

Maximum electrons in the N shell:

  1. (A) 18
  2. (B) 32
  3. (C) 50
  4. (D) 8
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Correct answer: (B) 32

Answer: 32.

54Book-based · 4.3 · p. 501 mark

The outermost shell can hold at most

  1. (A) 32
  2. (B) 2
  3. (C) 8
  4. (D) 18
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Correct answer: (C) 8

Answer: 8.

55Book-based · Table 4.1 · p. 511 mark

The electronic configuration of carbon (Z = 6) is

  1. (A) 4, 2
  2. (B) 2, 6
  3. (C) 6
  4. (D) 2, 4
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Correct answer: (D) 2, 4

Answer: 2, 4.

56Book-based · Table 4.1 · p. 511 mark

The configuration of chlorine (Z = 17) is

  1. (A) 2, 8, 7
  2. (B) 2, 7, 8
  3. (C) 8, 8, 1
  4. (D) 2, 8, 8
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Correct answer: (A) 2, 8, 7

Answer: 2, 8, 7.

57Book-based · Table 4.1 · p. 511 mark

According to Table 4.1, argon has ___ neutrons.

  1. (A) 20
  2. (B) 22
  3. (C) 40
  4. (D) 18
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Correct answer: (B) 22

Answer: 22.

58Book-based · Table 4.1 · p. 511 mark

In Table 4.1 the valency of phosphorus is

  1. (A) 1
  2. (B) 2
  3. (C) 3, 5
  4. (D) 4
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Correct answer: (C) 3, 5

Answer: 3, 5.

59Book-based · 4.4 · p. 511 mark

Electrons in the outermost shell are called

  1. (A) isotopes
  2. (B) α-particles
  3. (C) nucleons
  4. (D) valence electrons
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Correct answer: (D) valence electrons

Answer: valence electrons.

60Book-based · 4.4 · p. 511 mark

The outer shell of helium has

  1. (A) 2
  2. (B) 8
  3. (C) 0
  4. (D) 1
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Correct answer: (A) 2

Answer: 2.

61Book-based · 4.4 · p. 511 mark

Eight electrons in the outer shell are called

  1. (A) a nucleus
  2. (B) an octet
  3. (C) a pair
  4. (D) a triplet
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Correct answer: (B) an octet

Answer: an octet.

62Book-based · 4.4 · p. 511 mark

The valency of magnesium is

  1. (A) 8
  2. (B) 1
  3. (C) 2
  4. (D) 3
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Correct answer: (C) 2

Answer: 2.

63Book-based · 4.4 · p. 521 mark

Fluorine has valency 1 because it

  1. (A) gains 7 electrons
  2. (B) does nothing
  3. (C) loses 1 electron
  4. (D) gains 1 electron
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Correct answer: (D) gains 1 electron

Answer: gains 1 electron.

64Book-based · 4.4 · p. 521 mark

The valency of silicon (2, 8, 4) is

  1. (A) 4
  2. (B) 8
  3. (C) 0
  4. (D) 2
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Correct answer: (A) 4

Answer: 4.

65Book-based · 4.5 · p. 521 mark

Atomic number equals the number of

  1. (A) neutrons
  2. (B) protons
  3. (C) nucleons
  4. (D) mass number
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Correct answer: (B) protons

Answer: protons.

66Book-based · 4.5 · p. 521 mark

Atomic number is denoted by

  1. (A) n
  2. (B) A
  3. (C) Z
  4. (D) N
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Correct answer: (C) Z

Answer: Z.

67Book-based · 4.5 · p. 521 mark

Nucleons are

  1. (A) electrons and neutrons
  2. (B) protons only
  3. (C) electrons and protons
  4. (D) protons and neutrons
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Correct answer: (D) protons and neutrons

Answer: protons and neutrons.

68Book-based · 4.5 · p. 521 mark

The number of neutrons in ¹⁴₇N is

  1. (A) 7
  2. (B) 14
  3. (C) 21
  4. (D) 0
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Correct answer: (A) 7

Answer: 7.

69Book-based · 4.5 · p. 521 mark

In the notation ᴬ_Z X the upper number is the

  1. (A) atomic number
  2. (B) mass number
  3. (C) valency
  4. (D) electron count
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Correct answer: (B) mass number

Answer: mass number.

70Book-based · 4.6 · p. 521 mark

Deuterium has ___ neutron(s).

  1. (A) 3
  2. (B) 0
  3. (C) 1
  4. (D) 2
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Correct answer: (C) 1

Answer: 1.

71Book-based · 4.6 · p. 521 mark

Isotopes differ in the number of

  1. (A) electrons
  2. (B) atomic number
  3. (C) protons
  4. (D) neutrons
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Correct answer: (D) neutrons

Answer: neutrons.

72Book-based · 4.6 · p. 531 mark

Natural chlorine has ³⁵Cl and ³⁷Cl in the ratio

  1. (A) 3 : 1
  2. (B) 1 : 3
  3. (C) 2 : 1
  4. (D) 1 : 1
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Correct answer: (A) 3 : 1

Answer: 3 : 1.

73Book-based · 4.6 · p. 531 mark

The average atomic mass of chlorine is

  1. (A) 35 u
  2. (B) 35.5 u
  3. (C) 36 u
  4. (D) 37 u
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Correct answer: (B) 35.5 u

Answer: 35.5 u.

74Book-based · 4.6 · p. 531 mark

An isotope of which element is used to treat cancer?

  1. (A) iodine
  2. (B) uranium
  3. (C) cobalt
  4. (D) carbon
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Correct answer: (C) cobalt

Answer: cobalt.

75Book-based · 4.6 · p. 531 mark

An isotope of which element is fuel in nuclear reactors?

  1. (A) cobalt
  2. (B) iodine
  3. (C) hydrogen
  4. (D) uranium
Show answerHide answer

Correct answer: (D) uranium

Answer: uranium.

76Book-based · 4.6.1 · p. 531 mark

⁴⁰₂₀Ca and ⁴⁰₁₈Ar are

  1. (A) isobars
  2. (B) ions
  3. (C) molecules
  4. (D) isotopes
Show answerHide answer

Correct answer: (A) isobars

Answer: isobars.

77Book-based · 4.6.1 · p. 531 mark

Isobars have the same

  1. (A) atomic number
  2. (B) mass number
  3. (C) valency
  4. (D) electronic configuration
Show answerHide answer

Correct answer: (B) mass number

Answer: mass number.

78Book-based · Summary · p. 541 mark

Elements are defined by their number of

  1. (A) electron shells
  2. (B) neutrons
  3. (C) protons
  4. (D) mass
Show answerHide answer

Correct answer: (C) protons

Answer: protons.

← Chapter 4: Structure of the Atom — full notes, video, questions