Identify the substances that are oxidised and the substances that are reduced in the following reactions:
(i) 4Na (s) + O2 (g) → 2Na20 (s)
(ii) CuO (s) + H2 (g) → Cu (s) + H2O (l)
(i)
If a substance gain oxygen during a reaction, it is said to be oxidized. During this reaction, the sodium is gaining oxygen and is being oxidized. Oxygen is getting reduced.
(ii) 
During this reaction, copper oxide is losing oxygen and is being reduced. The hydrogen is gaining oxygen and is being oxidized.
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