Identify the substances that are oxidised and that are reduced in the following equation.
(i) 4Na(s) + O2(g) → 2Na2O(s)
(ii) CuO(s) + H2(g) → Cu(s) + H2O(l)

(i)With the addition of oxygen (O₂) in the first equation, the sodium (Na) gets oxidised, and O₂ is reduced.

(ii) In the second equation CuO is reduced and hydrogen (H₂) is oxidised.