Cement sets under water because of: MCQ with Answer and Explanation

Cement sets under water because of:
A. Evaporation
B. Hydration and hydrolysis of calcium silicates
C. Polymerization
D. Oxidation
Answer: Option B
Solution (By JKExamLibrary)
Cement sets by hydration reactions forming C-S-H gel and Ca(OH)₂, even underwater. It's a chemical process, not drying. Gypsum controls the setting rate.

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Question #1
Which of the following oxides is amphoteric?
A. Na₂O
B. Al₂O₃
C. MgO
D. SO₂

Correct Answer: Option B


Explanation:
Amphoteric oxides react with both acids and bases to form salts and water. Aluminum oxide (Al₂O₃) and Zinc oxide (ZnO) are classic examples. Na₂O and MgO are basic oxides that react only with acids, while SO₂ is an acidic oxide that reacts only with bases.

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Question #2
Which of the following is used as the electrolyte in a lead-acid storage battery?
A. Phosphoric acid
B. Sulphuric acid
C. Hydrochloric acid
D. Nitric acid

Correct Answer: Option B


Explanation:
A lead-acid battery, commonly used in automobiles, consists of lead anodes and lead dioxide cathodes. The electrolyte used is an aqueous solution of sulfuric acid (H2SO4). During discharge, the acid is consumed to form lead sulfate and water, decreasing the density of the electrolyte.

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Question #3
The half-life of a radioactive sample is 2 hours. What fraction remains after 6 hours?
A. 1/4
B. 1/16
C. 1/8
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Correct Answer: Option C


Explanation:
Number of half-lives = 6/2 = 3. Remaining = (1/2)³ = 1/8. After each half-life, half the remaining decays.

This question belongs to: Science chemistry