Chapter 9: Chemical Formula and Mole Concept – Important MCQs
1. The chemical formula of water is:
A. H₂O₂
B. HO
C. H₂O
D. H₃O
✔️ Answer: C. H₂O
2. The valency of oxygen is:
A. 1
B. 2
C. 3
D. 4
✔️ Answer: B. 2
3. The valency of an element is related to:
A. Number of protons
B. Atomic number
C. Number of outermost electrons
D. Number of neutrons
✔️ Answer: C. Number of outermost electrons
4. What is the chemical formula of sodium chloride?
A. NaCl₂
B. NaCl
C. Na₂Cl
D. Na₂Cl₂
✔️ Answer: B. NaCl
5. The molecular formula of ammonia is:
A. NH₄
B. NH₃
C. N₂H₄
D. N₂H
✔️ Answer: B. NH₃
6. What is the value of Avogadro’s number?
A. 6.022 × 10²³
B. 3.14 × 10²³
C. 9.8 × 10²
D. 6.022 × 10⁻²³
✔️ Answer: A. 6.022 × 10²³
7. One mole of a substance contains how many particles (atoms/molecules/ions)?
A. 1 × 10³
B. 6.022 × 10²³
C. 3.6 × 10²
D. 1 × 10⁶
✔️ Answer: B. 6.022 × 10²³
8. The formula mass of NaCl is:
A. 23
B. 35.5
C. 58.5
D. 60
✔️ Answer: C. 58.5
(23 for Na + 35.5 for Cl)
9. What is the unit of molar mass?
A. kg
B. g
C. g/mol
D. mol
✔️ Answer: C. g/mol
10. Which of the following formulas represents a compound?
A. H
B. O
C. O₂
D. HCl
✔️ Answer: D. HCl
