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Class 9 · Science · Chapter 3: Atoms and Molecules

BSEB Class 9 Science Chapter 3: Objective Questions (MCQ) with Answers

Bihar Board · NCERT · CBSE

All 72 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 3: Atoms and Molecules — full notes, video, questions

1Check1 mark

Who named the smallest particles "Parmanu"?

  1. (A) Democritus
  2. (B) Maharishi Kanad
  3. (C) Dalton
  4. (D) Lavoisier
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Correct answer: (B) Maharishi Kanad

Maharishi Kanad called the smallest particles Parmanu.

2Check1 mark

Mass of oxygen in 18 g of water is

  1. (A) 2 g
  2. (B) 8 g
  3. (C) 16 g
  4. (D) 9 g
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Correct answer: (C) 16 g

H : O = 1 : 8, so 18 g has 2 g H and 16 g O.

3Check1 mark

Which postulate of Dalton's theory results from the law of conservation of mass?

  1. (A) atoms of an element are identical
  2. (B) atoms are neither created nor destroyed
  3. (C) atoms combine in small whole numbers
  4. (D) atoms of different elements differ
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Correct answer: (B) atoms are neither created nor destroyed

Atoms are indivisible and are not created or destroyed in a reaction.

4Check1 mark

The radius of a hydrogen atom is about

  1. (A) 10⁻¹⁰ m
  2. (B) 10⁻⁸ m
  3. (C) 10⁻⁴ m
  4. (D) 10⁻² m
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Correct answer: (A) 10⁻¹⁰ m

In the relative-size table the H atom is 10⁻¹⁰ m.

5Check1 mark

The symbol K for potassium comes from

  1. (A) kalium
  2. (B) natrium
  3. (C) ferrum
  4. (D) krypton
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Correct answer: (A) kalium

From the Latin name kalium.

6Check1 mark

The present standard for atomic mass is

  1. (A) hydrogen-1
  2. (B) oxygen-16
  3. (C) carbon-12
  4. (D) nitrogen-14
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Correct answer: (C) carbon-12

Carbon-12 since 1961.

7Check1 mark

The atomicity of phosphorus is

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

P₄ — tetra-atomic.

8Check1 mark

The N : H mass ratio in ammonia is

  1. (A) 1 : 3
  2. (B) 14 : 3
  3. (C) 3 : 14
  4. (D) 1 : 8
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Correct answer: (B) 14 : 3

Table 3.4: 14 : 3.

9Check1 mark

Which of these is a cation?

  1. (A) Cl⁻
  2. (B) OH⁻
  3. (C) NH₄⁺
  4. (D) SO₄²⁻
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Correct answer: (C) NH₄⁺

The ammonium ion is positively charged.

10Check1 mark

The formula of aluminium oxide is

  1. (A) AlO
  2. (B) Al₂O₃
  3. (C) Al₃O₂
  4. (D) AlO₃
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Correct answer: (B) Al₂O₃

Criss-crossing Al³⁺ and O²⁻ gives Al₂O₃.

11Check1 mark

The molecular mass of CO₂ is

  1. (A) 28 u
  2. (B) 32 u
  3. (C) 44 u
  4. (D) 12 u
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Correct answer: (C) 44 u

12 + 2 × 16 = 44 u.

12Check1 mark

Number of moles in 22 g of CO₂ is

  1. (A) 0.5
  2. (B) 1
  3. (C) 2
  4. (D) 0.25
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Correct answer: (A) 0.5

M = 44 g; 22/44 = 0.5 mol.

13Book-based · Intro · p. 311 mark

When was the idea of divisibility of matter considered in India?

  1. (A) around 500 BC
  2. (B) 1808
  3. (C) 1961
  4. (D) 1896
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Correct answer: (A) around 500 BC

Answer: around 500 BC.

14Book-based · Intro · p. 311 mark

The word "atom" means

  1. (A) heavy
  2. (B) indivisible
  3. (C) charged
  4. (D) heap
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Correct answer: (B) indivisible

Answer: indivisible.

15Book-based · Intro · p. 311 mark

Who elaborated that these particles normally exist in a combined form?

  1. (A) Pakudha Katyayama
  2. (B) Democritus
  3. (C) Proust
  4. (D) Berzelius
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Correct answer: (A) Pakudha Katyayama

Answer: Pakudha Katyayama.

16Book-based · Intro · p. 311 mark

Who laid the foundation of chemical sciences?

  1. (A) Dalton
  2. (B) Lavoisier
  3. (C) Avogadro
  4. (D) Ostwald
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Correct answer: (B) Lavoisier

Answer: Lavoisier.

17Book-based · Activity 3.1 · p. 311 mark

In Activity 3.1 the solution of X is kept in

  1. (A) an ignition tube
  2. (B) a beaker
  3. (C) a test-tube stand
  4. (D) a separating funnel
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Correct answer: (A) an ignition tube

Answer: an ignition tube.

18Book-based · Activity 3.1 · p. 311 mark

In Activity 3.1 the solutions are of strength

  1. (A) 1%
  2. (B) 5%
  3. (C) 10%
  4. (D) 50%
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Correct answer: (B) 5%

Answer: 5%.

19Book-based · 3.1.1 · p. 321 mark

In a chemical reaction mass is

  1. (A) increased
  2. (B) decreased
  3. (C) neither created nor destroyed
  4. (D) halved
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Correct answer: (C) neither created nor destroyed

Answer: neither created nor destroyed.

20Book-based · 3.1.2 · p. 321 mark

The mass ratio of hydrogen to oxygen in water is

  1. (A) 2 : 1
  2. (B) 1 : 8
  3. (C) 8 : 1
  4. (D) 1 : 16
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Correct answer: (B) 1 : 8

Answer: 1 : 8.

21Book-based · 3.1.2 · p. 321 mark

Decomposing 9 g of water gives hydrogen

  1. (A) 1 g
  2. (B) 2 g
  3. (C) 8 g
  4. (D) 9 g
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Correct answer: (A) 1 g

Answer: 1 g.

22Book-based · 3.1.2 · p. 321 mark

The law of constant proportions was stated by

  1. (A) Lavoisier
  2. (B) Proust
  3. (C) Dalton
  4. (D) Kanad
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Correct answer: (B) Proust

Answer: Proust.

23Book-based · 3.1.2 · p. 321 mark

Dalton was born in

  1. (A) 1766
  2. (B) 1808
  3. (C) 1793
  4. (D) 1896
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Correct answer: (A) 1766

Answer: 1766.

24Book-based · 3.1.2 · p. 321 mark

Dalton presented his atomic theory in

  1. (A) 1766
  2. (B) 1793
  3. (C) 1808
  4. (D) 1961
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Correct answer: (C) 1808

Answer: 1808.

25Book-based · 3.1.2 · p. 321 mark

According to Dalton, atoms combine to form compounds in

  1. (A) fractional ratios
  2. (B) ratios of small whole numbers
  3. (C) any ratio
  4. (D) only 1 : 1
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Correct answer: (B) ratios of small whole numbers

Answer: ratios of small whole numbers.

26Book-based · 3.1.2 · p. 321 mark

Which Dalton postulate explains the law of definite proportions?

  1. (A) atoms are indivisible
  2. (B) the relative number and kinds of atoms in a compound are constant
  3. (C) all matter is made of atoms
  4. (D) atoms of different elements differ
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Correct answer: (B) the relative number and kinds of atoms in a compound are constant

Answer: the relative number and kinds of atoms in a compound are constant.

27Book-based · 3.2 · p. 331 mark

1 nm equals

  1. (A) 10⁻⁶ m
  2. (B) 10⁻⁹ m
  3. (C) 10⁻¹² m
  4. (D) 10⁹ m
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Correct answer: (B) 10⁻⁹ m

Answer: 10⁻⁹ m.

28Book-based · 3.2 · p. 331 mark

The radius of a water molecule is about

  1. (A) 10⁻¹⁰ m
  2. (B) 10⁻⁹ m
  3. (C) 10⁻⁸ m
  4. (D) 10⁻⁴ m
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Correct answer: (B) 10⁻⁹ m

Answer: 10⁻⁹ m.

29Book-based · 3.2 · p. 331 mark

The radius of a haemoglobin molecule is about

  1. (A) 10⁻⁸ m
  2. (B) 10⁻¹⁰ m
  3. (C) 10⁻² m
  4. (D) 10⁻¹ m
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Correct answer: (A) 10⁻⁸ m

Answer: 10⁻⁸ m.

30Book-based · Fig. 3.2 · p. 331 mark

Fig. 3.2 shows an image of the surface of

  1. (A) gold
  2. (B) silicon
  3. (C) carbon
  4. (D) iron
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Correct answer: (B) silicon

Answer: silicon.

31Book-based · 3.2.1 · p. 331 mark

Who first used a symbol to mean one atom of the element?

  1. (A) Berzelius
  2. (B) Dalton
  3. (C) IUPAC
  4. (D) Proust
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Correct answer: (B) Dalton

Answer: Dalton.

32Book-based · 3.2.1 · p. 331 mark

Who suggested symbols from one or two letters of the name?

  1. (A) Berzelius
  2. (B) Dalton
  3. (C) Lavoisier
  4. (D) Avogadro
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Correct answer: (A) Berzelius

Answer: Berzelius.

33Book-based · 3.2.1 · p. 341 mark

The name copper was taken from

  1. (A) Cyprus
  2. (B) Cuba
  3. (C) China
  4. (D) Egypt
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Correct answer: (A) Cyprus

Answer: Cyprus.

34Book-based · 3.2.1 · p. 341 mark

Who approves names of elements today?

  1. (A) IUPAC
  2. (B) NCERT
  3. (C) ISRO
  4. (D) UNESCO
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Correct answer: (A) IUPAC

Answer: IUPAC.

35Book-based · 3.2.1 · p. 341 mark

The correct symbol of aluminium is

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

Answer: Al.

36Book-based · 3.2.1 · p. 341 mark

The symbol Na for sodium comes from

  1. (A) natrium
  2. (B) soda
  3. (C) neon
  4. (D) nitrum
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Correct answer: (A) natrium

Answer: natrium.

37Book-based · Table 3.1 · p. 341 mark

The symbol of silver is

  1. (A) Si
  2. (B) Ag
  3. (C) Au
  4. (D) S
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Correct answer: (B) Ag

Answer: Ag.

38Book-based · Table 3.1 · p. 341 mark

The symbol of lead is

  1. (A) Le
  2. (B) L
  3. (C) Pb
  4. (D) Ld
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Correct answer: (C) Pb

Answer: Pb.

39Book-based · 3.2.2 · p. 341 mark

To form CO, 3 g of carbon combines with oxygen

  1. (A) 3 g
  2. (B) 4 g
  3. (C) 8 g
  4. (D) 16 g
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Correct answer: (B) 4 g

Answer: 4 g.

40Book-based · 3.2.2 · p. 351 mark

Carbon-12 was chosen as the universal standard in

  1. (A) 1808
  2. (B) 1896
  3. (C) 1961
  4. (D) 1967
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Correct answer: (C) 1961

Answer: 1961.

41Book-based · 3.2.2 · p. 351 mark

Earlier the unit was what fraction of an oxygen atom's mass?

  1. (A) 1/12
  2. (B) 1/16
  3. (C) 1/8
  4. (D) 1/2
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Correct answer: (B) 1/16

Answer: 1/16.

42Book-based · Table 3.2 · p. 351 mark

The atomic mass of magnesium is

  1. (A) 12 u
  2. (B) 24 u
  3. (C) 23 u
  4. (D) 40 u
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Correct answer: (B) 24 u

Answer: 24 u.

43Book-based · Table 3.2 · p. 351 mark

The atomic mass of sulphur is

  1. (A) 16 u
  2. (B) 32 u
  3. (C) 35.5 u
  4. (D) 64 u
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Correct answer: (B) 32 u

Answer: 32 u.

44Book-based · 3.3 · p. 351 mark

The smallest particle of an element or compound capable of independent existence is

  1. (A) an atom
  2. (B) a molecule
  3. (C) an ion
  4. (D) an electron
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Correct answer: (B) a molecule

Answer: a molecule.

45Book-based · 3.3.1 · p. 361 mark

The atomicity of argon is

  1. (A) monoatomic
  2. (B) diatomic
  3. (C) tetra-atomic
  4. (D) poly-atomic
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Correct answer: (A) monoatomic

Answer: monoatomic.

46Book-based · 3.3.1 · p. 361 mark

An ozone molecule has how many oxygen atoms?

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

Answer: 3.

47Book-based · Table 3.3 · p. 361 mark

Sulphur is

  1. (A) monoatomic
  2. (B) diatomic
  3. (C) tetra-atomic
  4. (D) poly-atomic
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Correct answer: (D) poly-atomic

Answer: poly-atomic.

48Book-based · Table 3.4 · p. 361 mark

The C : O mass ratio in CO₂ is

  1. (A) 1 : 2
  2. (B) 3 : 8
  3. (C) 8 : 3
  4. (D) 12 : 16
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Correct answer: (B) 3 : 8

Answer: 3 : 8.

49Book-based · 3.3.3 · p. 361 mark

A negatively charged ion is called

  1. (A) a cation
  2. (B) an anion
  3. (C) a molecule
  4. (D) an isotope
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Correct answer: (B) an anion

Answer: an anion.

50Book-based · Table 3.5 · p. 371 mark

The Ca : O mass ratio in calcium oxide is

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

Answer: 5 : 2.

51Book-based · Table 3.5 · p. 371 mark

The Mg : S mass ratio in magnesium sulphide is

  1. (A) 3 : 4
  2. (B) 4 : 3
  3. (C) 5 : 2
  4. (D) 23 : 35.5
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Correct answer: (A) 3 : 4

Answer: 3 : 4.

52Book-based · Table 3.6 · p. 371 mark

The sulphate ion is

  1. (A) SO₃²⁻
  2. (B) SO₄²⁻
  3. (C) S²⁻
  4. (D) HSO₄⁻
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Correct answer: (B) SO₄²⁻

Answer: SO₄²⁻.

53Book-based · Table 3.6 · p. 371 mark

The valency of the nitride ion is

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

Answer: 3.

54Book-based · Table 3.6 · p. 371 mark

The iron (III) ion is

  1. (A) Fe²⁺
  2. (B) Fe³⁺
  3. (C) Fe⁺
  4. (D) Fe⁴⁺
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Correct answer: (B) Fe³⁺

Answer: Fe³⁺.

55Book-based · 3.4 · p. 371 mark

The formula in the octopus–human example is

  1. (A) O₄H
  2. (B) OH₄
  3. (C) OH₂
  4. (D) O₂H
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Correct answer: (B) OH₄

Answer: OH₄.

56Book-based · 3.4 · p. 381 mark

In a metal–non-metal compound, which is written first?

  1. (A) the non-metal
  2. (B) the metal
  3. (C) the bigger atom
  4. (D) either
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Correct answer: (B) the metal

Answer: the metal.

57Book-based · 3.4.1 · p. 381 mark

The formula of magnesium chloride is

  1. (A) MgCl
  2. (B) Mg₂Cl
  3. (C) MgCl₂
  4. (D) Mg₂Cl₂
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Correct answer: (C) MgCl₂

Answer: MgCl₂.

58Book-based · 3.4.1 · p. 381 mark

The formula of carbon tetrachloride is

  1. (A) CCl₄
  2. (B) C₄Cl
  3. (C) CCl₂
  4. (D) C₂Cl₄
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Correct answer: (A) CCl₄

Answer: CCl₄.

59Book-based · 3.4.1 · p. 391 mark

The formula of ammonium sulphate is

  1. (A) NH₄SO₄
  2. (B) (NH₄)₂SO₄
  3. (C) NH₄(SO₄)₂
  4. (D) (NH₄)₃SO₄
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Correct answer: (B) (NH₄)₂SO₄

Answer: (NH₄)₂SO₄.

60Book-based · 3.4.1 · p. 391 mark

The formula of sodium carbonate is

  1. (A) NaCO₃
  2. (B) Na₂CO₃
  3. (C) Na(CO₃)₂
  4. (D) Na₂(CO₃)₂
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Correct answer: (B) Na₂CO₃

Answer: Na₂CO₃.

61Book-based · Example 3.1 · p. 391 mark

The molecular mass of HNO₃ is

  1. (A) 63 u
  2. (B) 62 u
  3. (C) 48 u
  4. (D) 31 u
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Correct answer: (A) 63 u

Answer: 63 u.

62Book-based · 3.5.2 · p. 401 mark

The formula unit mass of NaCl is

  1. (A) 58.5 u
  2. (B) 23 u
  3. (C) 35.5 u
  4. (D) 117 u
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Correct answer: (A) 58.5 u

Answer: 58.5 u.

63Book-based · Example 3.2 · p. 401 mark

The formula unit mass of CaCl₂ is

  1. (A) 75.5 u
  2. (B) 111 u
  3. (C) 110 u
  4. (D) 95.5 u
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Correct answer: (B) 111 u

Answer: 111 u.

64Book-based · 3.5.3 · p. 411 mark

The value of the Avogadro number is

  1. (A) 6.022 × 10²³
  2. (B) 6.022 × 10²²
  3. (C) 3.011 × 10²³
  4. (D) 12 × 10²³
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Correct answer: (A) 6.022 × 10²³

Answer: 6.022 × 10²³.

65Book-based · 3.5.3 · p. 411 mark

Who introduced the word "mole"?

  1. (A) Avogadro
  2. (B) Wilhelm Ostwald
  3. (C) Dalton
  4. (D) Berzelius
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Correct answer: (B) Wilhelm Ostwald

Answer: Wilhelm Ostwald.

66Book-based · 3.5.3 · p. 411 mark

The mole unit was accepted in

  1. (A) 1896
  2. (B) 1961
  3. (C) 1967
  4. (D) 1808
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Correct answer: (C) 1967

Answer: 1967.

67Book-based · 3.5.3 · p. 411 mark

Number of molecules in 18 g of water is

  1. (A) 6.022 × 10²³
  2. (B) 18 × 10²³
  3. (C) 3.011 × 10²³
  4. (D) 1
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Correct answer: (A) 6.022 × 10²³

Answer: 6.022 × 10²³.

68Book-based · Example 3.3 · p. 411 mark

Moles in 52 g of helium

  1. (A) 4
  2. (B) 13
  3. (C) 26
  4. (D) 52
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Correct answer: (B) 13

Answer: 13.

69Book-based · Example 3.4 · p. 421 mark

Mass of 0.5 mole of N₂ gas

  1. (A) 7 g
  2. (B) 14 g
  3. (C) 28 g
  4. (D) 56 g
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Correct answer: (B) 14 g

Answer: 14 g.

70Book-based · Example 3.4 · p. 421 mark

Mass of 0.5 mole of N atoms

  1. (A) 7 g
  2. (B) 14 g
  3. (C) 28 g
  4. (D) 3.5 g
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Correct answer: (A) 7 g

Answer: 7 g.

71Book-based · Example 3.5 · p. 421 mark

Atoms in 46 g of sodium

  1. (A) 6.022 × 10²³
  2. (B) 12.044 × 10²³
  3. (C) 3.011 × 10²³
  4. (D) 46 × 10²³
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Correct answer: (B) 12.044 × 10²³

Answer: 12.044 × 10²³.

72Book-based · Example 3.5 · p. 421 mark

Atoms in 0.1 mole of carbon

  1. (A) 6.022 × 10²²
  2. (B) 6.022 × 10²³
  3. (C) 6.022 × 10²⁴
  4. (D) 1.2 × 10²³
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Correct answer: (A) 6.022 × 10²²

Answer: 6.022 × 10²².

← Chapter 3: Atoms and Molecules — full notes, video, questions