State reasons for the following :
(i) Aluminium oxide is called an amphoteric oxide.
(ii) Hydrogen gas is not evolved when most metals react with nitric acid.
(iii) Nitrogen is used to preserve food.

Explanation

(i) Aluminium reacts with acids as well as bases, therefore it is called amphoteric oxide.
(ii) Nitric acid is a strong oxidsing agent. Hence, it oxides the hydrogen formed during the reaction to water.
(iii) Nitrogen prevents food from getting oxidised due to its inert nature hence it is used as a preservative.