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Solution


Q.

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.
1 (i) and (iv)  
2 (ii) and (iii)  
3 (i) and (ii)  
4 (iii) and (iv)  

Ans.

(4)

Calcium metal reacts less violently with water. It produces a hydroxide known as calcium hydroxide (a cloudy white precipitate), and bubbles of hydrogen gas are produced.
The hydrogen gas thus produced sticks to the surface of calcium due to which it floats over the water surface.

Ca(s) + 2H2O(l)→Ca(OH)2​(aq)+H2​↑
                                      Calcium hydroxide

very less amount of heat is produced in this reaction due to which hydrogen gas formed does not catch fire.