Identify the substances that are oxidised and the substances that are reduced in the following reactions.
(i) `4Na(s)+O_(2)(g)rarr2NaO(s)`
(ii) `CuO(g) +H_(2)(g) rarr Cu(s) +H_(2)O(l)`

Explanation

To identify the substances that are oxidized and reduced in the given reactions, we need to analyze the changes in oxidation states of the elements involved. Let's break down each reaction step by step.

### Reaction (i):
`4Na(s) + O2(g) → 2Na2O(s)`

**Step 1: Determine the oxidation states of the reactants and products.**
- Sodium (Na) in its elemental form has an oxidation state of 0.
- Oxygen (O2) in its elemental form also has an oxidation state of 0.
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