a. When calcium metal is added to water, the gas evolved does not catch fire but the same gas evolved on adding potassium metal to water catches fire. Explain.
b. Name a metal for each case:
(i) It displaces hydrogen gas from nitric acid.
(ii) It does not react with any physical state of water
(iii) It reacts with neither cold nor hot water, but reacts with steam.

Explanation

a. Calcium is less reactive than potassium, hence the reaction of calcium with water is less vigorous and the energy liberated is also low, whereas the same reaction with potassium is highly exothermic, hence the evolving gas catches fire.
b. (i) Magnesium/ Manganese
(ii) Copper/gold/ platinum.
(iii) Iron/ Zinc.