Class 9 Science Chapter 9 MCQ
Chapter 9: Atomic Foundation of Matter
50 MCQs | 5 Sets
Practise important laws, atomic theory, molecules, chemical bonds, ions and chemical formulae.
Set 1: Laws of Chemical Combination
Questions 1–10
1. According to the law of conservation of mass, mass in a chemical reaction is:
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Answer: (C) Neither created nor destroyed
2. Who proposed the law of conservation of mass?
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Answer: (B) Antoine Lavoisier
3. In a closed system, the total mass of reactants is:
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Answer: (C) Equal to the product mass
4. When baking soda reacts with vinegar, which gas is produced?
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Answer: (C) Carbon dioxide
5. In an open flask, the measured mass may decrease during a reaction that produces a gas because:
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Answer: (B) The gas escapes into the surroundings
6. Who proposed the law of constant proportions?
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Answer: (A) Joseph Proust
7. The law of constant proportions is also known as the:
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Answer: (B) Law of definite proportions
8. According to the law of constant proportions, a pure compound always contains its elements in:
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Answer: (A) A fixed ratio by mass
9. What is the mass ratio of hydrogen to oxygen in pure water?
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Answer: (C) 1:8
10. How much oxygen combines with 3 g of hydrogen to form water completely?
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Answer: (D) 24 g. The hydrogen-to-oxygen mass ratio is 1:8.
Set 2: Dalton's Atomic Theory
Questions 11–20
11. John Dalton proposed his atomic theory in:
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Answer: (B) 1808
12. According to Dalton's theory, all matter is made up of tiny particles called:
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Answer: (B) Atoms
13. According to Dalton's original theory, atoms were considered:
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Answer: (A) Indivisible particles
14. According to Dalton, atoms of the same element were considered to have:
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Answer: (B) Identical masses and chemical properties, according to the original theory
15. Atoms of different elements generally differ in their:
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Answer: (C) Both (A) and (B)
16. According to Dalton's theory, atoms combine to form compounds in:
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Answer: (B) Simple whole-number ratios
17. During a chemical reaction, atoms are mainly:
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Answer: (C) Rearranged
18. Which statement about atoms is correct?
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Answer: (B) Atoms contain a nucleus and electrons
19. A molecule is a group of atoms held together by:
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Answer: (A) Chemical bonds
20. Which of the following is a molecule of an element?
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Answer: (C) H₂
Set 3: Molecules and Covalent Bonds
Questions 21–30
21. A molecule is generally an electrically:
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Answer: (C) Neutral entity
22. A covalent bond is formed by:
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Answer: (A) Sharing electrons
23. How many covalent bonds are present in a hydrogen molecule, H₂?
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Answer: (A) One single bond
24. How many valence electrons does a chlorine atom have?
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Answer: (C) 7
25. A chlorine molecule, Cl₂, contains:
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Answer: (A) One shared pair of electrons
26. The bond in an oxygen molecule, O₂, is a:
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Answer: (B) Double covalent bond
27. What is the chemical formula of hydrogen chloride?
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Answer: (B) HCl
28. In a hydrogen chloride molecule, hydrogen and chlorine are held together by:
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Answer: (A) Sharing electrons
29. One molecule of water contains:
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Answer: (B) Two hydrogen and one oxygen atom
30. The force that holds atoms together in a molecule is associated with a:
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Answer: (A) Chemical bond
Set 4: Ions and Ionic Compounds
Questions 31–40
31. An ionic bond is formed mainly through:
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Answer: (B) Transfer of electrons followed by electrostatic attraction
32. When a sodium atom loses one electron, it forms:
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Answer: (B) Na⁺
33. When a chlorine atom gains one electron, it forms:
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Answer: (C) Cl⁻
34. Positively charged ions are called:
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Answer: (B) Cations
35. Negatively charged ions are called:
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Answer: (B) Anions
36. The electrostatic attraction between oppositely charged ions is called:
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Answer: (B) Ionic bonding
37. What is the chemical formula of sodium chloride?
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Answer: (A) NaCl
38. Which of the following is a polyatomic ion?
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Answer: (D) SO₄²⁻
39. What is the correct formula for magnesium hydroxide?
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Answer: (B) Mg(OH)₂
40. What is the correct chemical formula for aluminium sulfate?
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Answer: (D) Al₂(SO₄)₃
Set 5: Chemical Formulae and Formula Mass
Questions 41–50
41. What is the molecular mass of water (H₂O)? Take H = 1 u and O = 16 u.
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Answer: (C) 18 u. Molecular mass = 2 × 1 + 16 = 18 u.
42. What is the formula unit mass of sodium oxide (Na₂O)? Take Na = 23 u and O = 16 u.
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Answer: (D) 62 u. Formula unit mass = 2 × 23 + 16 = 62 u.
43. What is the formula unit mass of calcium nitrate, Ca(NO₃)₂? Take Ca = 40 u, N = 14 u and O = 16 u.
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Answer: (C) 164 u. Mass = 40 + 2 × (14 + 3 × 16) = 164 u.
44. What is the formula unit mass of sodium chloride (NaCl)? Take Na = 23 u and Cl = 35.5 u.
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Answer: (C) 58.5 u
45. What is the molecular mass of carbon dioxide (CO₂)? Take C = 12 u and O = 16 u.
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Answer: (D) 44 u
46. What is the correct formula for calcium chloride?
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Answer: (B) CaCl₂
47. What is the correct formula for aluminium oxide?
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Answer: (C) Al₂O₃
48. What is the chemical formula of ammonium sulfate?
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Answer: (B) (NH₄)₂SO₄
49. What is the molecular mass of ammonia (NH₃)? Take N = 14 u and H = 1 u.
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Answer: (C) 17 u. Molecular mass = 14 + 3 × 1 = 17 u.
50. What is the formula unit mass of magnesium oxide (MgO)? Take Mg = 24 u and O = 16 u.
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Answer: (C) 40 u