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Explanation: Antoine Lavoisier established the Law of Conservation of Mass, which states that mass can neither be created nor destroyed in a chemical reaction.
2. In a chemical compound like water (H₂O), the ratio of the mass of hydrogen to oxygen is always:
A. 1 : 8
B. 8 : 1
C. 1 : 2
D. 2 : 1
Answer: A. 1 : 8
Explanation: According to the Law of Constant Proportions, water always contains hydrogen and oxygen combined in a fixed mass ratio of 1:8 (2g of H to 16g of O).
3. One atomic mass unit (1 u) is defined as a mass unit equal to exactly one-twelfth the mass of one atom of:
A. Carbon-12
B. Hydrogen-1
C. Oxygen-16
D. Nitrogen-14
Answer: A. Carbon-12
Explanation: Carbon-12 isotope is taken as the standard reference for measuring atomic masses. 1 u = 1/12th the mass of one C-12 atom.
4. What is the Latin name of Sodium from which its chemical symbol 'Na' is derived?
A. Kalium
B. Natrium
C. Ferrum
D. Cuprum
Answer: B. Natrium
Explanation: The symbol Na for Sodium comes from its Latin name 'Natrium'. (Similarly, Kalium = K, Ferrum = Fe, Cuprum = Cu).
5. What is the relative molecular mass of Water (H₂O)?
A. 16 u
B. 18 u
C. 20 u
D. 32 u
Answer: B. 18 u
Explanation: Atomic mass of H = 1 u, O = 16 u. Molecular mass of H₂O = (2 × 1) + 16 = 18 u.
6. What is the chemical formula of Calcium Carbonate?
A. CaCO₃
B. Ca(OH)₂
C. CaCl₂
D. CaO
Answer: A. CaCO₃
Explanation: Calcium has a valency of +2 (Ca²⁺) and Carbonate has a valency of -2 (CO₃²⁻). Combining them gives CaCO₃.
7. What is the atomicity of Ozone (O₃)?
A. Monoatomic
B. Diatomic
C. Triatomic
D. Polyatomic (4+)
Answer: C. Triatomic
Explanation: Atomicity refers to the number of atoms constituting a molecule. Ozone consists of 3 oxygen atoms, making it triatomic.
8. What is the value of Avogadro's constant (Nₐ)?
A. 6.022 × 10²³
B. 6.022 × 10²²
C. 3.011 × 10²³
D. 1.66 × 10⁻²⁴
Answer: A. 6.022 × 10²³
Explanation: One mole of any substance contains a fixed number of particles, known as Avogadro's constant = 6.022 × 10²³ per mole.
9. Which of the following is a polyatomic ion?
A. Na⁺
B. Cl⁻
C. NH₄⁺
D. Mg²⁺
Answer: C. NH₄⁺
Explanation: Ammonium (NH₄⁺) is composed of a group of atoms carrying a net charge, making it a polyatomic ion.
10. What is the mass of 1 mole of Nitrogen gas (N₂)?
A. 14 g
B. 28 g
C. 7 g
D. 56 g
Answer: B. 28 g
Explanation: Atomic mass of N = 14 u. Molar mass of N₂ gas = 2 × 14 = 28 g/mol.
This page contains a chapter-wise objective practice set. Try the questions without checking the answer first, then use the explanation to understand the point you missed. The current page contains 10 questions, so you can practise in smaller sets when you are revising.
Quick revision tip
After the practice set, write down the question numbers you missed and revise only those concepts once more. This makes MCQ practice more useful than repeatedly attempting the same questions without reviewing mistakes.
