Question

What happens when calcium is treated with water?

(i) It does not react with water.
(ii) It reacts violently with water.
(iii) It reacts less violently with water.
(iv) Bubbles of hydrogen gas formed stick to the surface of calcium.

• A. (i) and (iv)
• B. (ii) and (iii)
• C. (i) and (ii)
• D. (iii) and (iv)

Answer 1

The correct option is D (iii) and (iv)

Calcium doesn't undergo violent reaction with water. Though it is exothermic, the heat evolved is not sufficient for the hydrogen to catch fire.

$\text{Ca(s)}+2{\text{H}}_2\text{O(l)}\to {\text{Ca(OH)}}_2\text{(aq)}+{\text{H}}_2\text{(g)}$

Calcium starts floating because the bubbles of hydrogen gas formed during the reaction stick to its surface and lifts it up.