Complete and balance the following equations :
(i) `Na + O_(2) to`
(ii) `Na_(2)O + H_(2)O to `
(iii) `Cu + HCl to`
(iv) `Cu^(2+) + Zn to`

Explanation

Let's solve and balance the equations step by step:

### (i) \( \text{Na} + \text{O}_2 \rightarrow \text{Na}_2\text{O} \)

1. **Write the unbalanced equation**:
\[ \text{Na} + \text{O}_2 \rightarrow \text{Na}_2\text{O} \]
...