(a) (i) Oxidation is the gain of oxygen.
Example:
2Mg + O2 → 2MgO
Here, Mg is oxidised to MgO by accepting oxygen.
(ii) Reduction is the loss of oxygen.
Example:
ZnO + C → Zn + CO
Here, ZnO is reduced to Zn by losing oxygen.
(b) Balanced chemical reaction is as follows:
2Cu + O2 → 2CuO
(i) The substance oxidised is copper.
(ii) The substance reduced is oxygen.