Identify the substances that are oxidised and the substances that are reduced in the following reactions.
(i) \( 4Na (s)+ O_2 (g) → 2Na_2 O(s) \)

(ii) \( CuO(s) + H_2 (g) → Cu(s) +H_2 O(l) \)

(i)In the given reaction, Sodium gains and combines with oxygen hence it is oxidised. Consequently Oxygen is getting reduced.

(ii)In this reaction Hydrogen gains Oxygen and forms water, hence it is getting oxidised. And on the other hand Copper is losing Oxygen hence, getting reduced.