Extra 40 MCQs with answers from the chapter:3 "Atoms and Molecules" for Class 9 CBSE Science:-
Multiple Choice Questions (MCQs)
1. Who gave the law of conservation of mass?
A) Dalton
B) Lavoisier
C) Avogadro
D) Rutherford
Answer: B) Lavoisier
2. What does the law of conservation of mass state?
A) Matter can be created
B) Matter can be destroyed
C) Mass remains constant in a chemical reaction
D) Energy is always lost in a reaction
Answer: C) Mass remains constant in a chemical reaction
3. Which scientist proposed the law of constant proportions?
A) Dalton
B) Lavoisier
C) Proust
D) Rutherford
Answer: C) Proust
4. What does the law of constant proportions state?
A) A chemical compound always contains its elements in a fixed proportion
B) The total mass of reactants and products remains the same
C) Atoms cannot be created or destroyed
D) Elements combine in multiple ratios
Answer: A) A chemical compound always contains its elements in a fixed proportion
5. Who proposed the atomic theory?
A) J.J. Thomson
B) John Dalton
C) Ernest Rutherford
D) Neils Bohr
Answer: B) John Dalton
6. What is the smallest particle of an element that retains its identity?
A) Molecule
B) Ion
C) Atom
D) Compound
Answer: C) Atom
7. Which subatomic particle has a negative charge?
A) Proton
B) Neutron
C) Electron
D) Nucleus
Answer: C) Electron
8. What is the charge of a proton?
A) Neutral
B) Positive
C) Negative
D) No charge
Answer: B) Positive
9. Which subatomic particle has no charge?
A) Proton
B) Neutron
C) Electron
D) Nucleus
Answer: B) Neutron
10. What is the mass of 1 mole of oxygen atoms?
A) 8 g
B) 16 g
C) 32 g
D) 18 g
Answer: B) 16 g
11. What is Avogadro’s number?
A) 6.022×10206.022 \times 10^{20}6.022×1020
B) 6.022×10236.022 \times 10^{23}6.022×1023
C) 6.022×10266.022 \times 10^{26}6.022×1026
D) 6.022×10306.022 \times 10^{30}6.022×1030
Answer: B) 6.022×10236.022 \times 10^{23}6.022×1023
12. What is a molecule?
A) The smallest unit of a compound
B) The smallest unit of an element
C) A charged particle
D) A neutral atom
Answer: A) The smallest unit of a compound
13. Which of the following is a diatomic molecule?
A) O₂
B) NaCl
C) CO₂
D) H₂O
Answer: A) O₂
14. What is the molecular formula of water?
A) H₂O₂
B) H₂O
C) H₂O₃
D) HO
Answer: B) H₂O
15. Which of the following is a polyatomic ion?
A) Na⁺
B) Cl⁻
C) SO₄²⁻
D) O₂
Answer: C) SO₄²⁻
16. The atomic number of an element represents the number of:
A) Protons
B) Neutrons
C) Electrons
D) Both A and C
Answer: D) Both A and C
17. What is the molecular mass of CO₂?
A) 44 g/mol
B) 12 g/mol
C) 32 g/mol
D) 28 g/mol
Answer: A) 44 g/mol
18. The chemical formula of Ammonium sulphate is:
A) NH₄SO₄
B) (NH₄)₂SO₄
C) NH₃SO₄
D) NH₄(SO₄)₂
Answer: B) (NH₄)₂SO₄
19. The symbol of gold is:
A) Ag
B) Au
C) Gd
D) Go
Answer: B) Au
20. One mole of any substance contains how many particles?
A) 6.022×10206.022 \times 10^{20}6.022×1020
B) 6.022×10236.022 \times 10^{23}6.022×1023
C) 6.022×10266.022 \times 10^{26}6.022×1026
D) 6.022×10306.022 \times 10^{30}6.022×1030
Answer: B) 6.022×10236.022 \times 10^{23}6.022×1023
21. What is the valency of oxygen?
A) 1
B) 2
C) 3
D) 4
Answer: B) 2
22. The atomic mass of magnesium (Mg) is:
A) 12
B) 24
C) 32
D) 40
Answer: B) 24
23. Which law explains that atoms cannot be created or destroyed?
A) Law of conservation of mass
B) Law of definite proportions
C) Law of multiple proportions
D) Avogadro’s law
Answer: A) Law of conservation of mass
24. The formula of quicklime is:
A) CaO
B) Ca(OH)₂
C) CaCO₃
D) CaCl₂
Answer: A) CaO
25. How many hydrogen atoms are in H₂SO₄?
A) 1
B) 2
C) 4
D) 6
Answer: B) 2
26. The molecular mass of NH₃ is:
A) 14 g/mol
B) 17 g/mol
C) 18 g/mol
D) 16 g/mol
Answer: B) 17 g/mol
27. What is the formula of Baking Soda?
A) Na₂CO₃
B) NaHCO₃
C) NaCl
D) NaOH
Answer: B) NaHCO₃
28. The atomic number of carbon is:
A) 6
B) 12
C) 14
D) 16
Answer: A) 6
29. The atomic mass of hydrogen is:
A) 1 u
B) 2 u
C) 4 u
D) 8 u
Answer: A) 1 u
30. The molecular formula of methane is:
A) CH₄
B) C₂H₆
C) C₃H₈
D) C₄H₁₀
Answer: A) CH₄
31. Which of the following has the highest atomic mass?
A) Oxygen
B) Carbon
C) Hydrogen
D) Sulphur
Answer: D) Sulphur
32. The atomicity of phosphorus (P₄) is:
A) 1
B) 2
C) 4
D) 8
Answer: C) 4
33. Which of the following is a triatomic molecule?
A) H₂
B) O₂
C) CO₂
D) NaCl
Answer: C) CO₂
34. What is the mass of one mole of nitrogen gas (N₂)?
A) 7 g
B) 14 g
C) 28 g
D) 32 g
Answer: C) 28 g
35. What is the formula of rust?
A) Fe₂O₃
B) Fe₂O₃·xH₂O
C) FeO
D) Fe₃O₄
Answer: B) Fe₂O₃·xH₂O
36. Which of the following is a molecular formula?
A) O
B) O₂
C) O³
D) O₄
Answer: B) O₂
37. The gram atomic mass of chlorine is:
A) 17 g
B) 35.5 g
C) 37 g
D) 40 g
Answer: B) 35.5 g
38. The ratio of hydrogen to oxygen in water (H₂O) by mass is:
A) 1:8
B) 2:1
C) 8:1
D) 1:2
Answer: A) 1:8
39. What is the molecular mass of NaCl?
A) 35.5 u
B) 58.5 u
C) 60 u
D) 40 u
Answer: B) 58.5 u
40. Which of the following statements about an atom is correct?
A) Atoms are indivisible and cannot be broken down further.
B) Atoms combine in simple whole number ratios to form compounds.
C) The mass of an atom is equally distributed throughout.
D) Atoms do not take part in chemical reactions.
Answer: B) Atoms combine in simple whole number ratios to form compounds.
