Identify the substances that are oxidised and
Question.
Identify the substances that are oxidised and the substances that are reduced in the following reactions.

(i) $4 \mathrm{Na}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{Na}_{2} \mathrm{O}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{~g})$

(ii) $\mathrm{CuO}(\mathrm{s})+\mathrm{H}_{2}(\mathrm{~g}) \rightarrow \mathrm{Cu}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\ell)$

solution:
(i) Sodium (Na) is oxidised as it gains oxygen and oxygen gets reduced.

(ii) Copper oxide $(\mathrm{CuO})$ is reduced to copper $(\mathrm{Cu})$ while hydrogen $\left(\mathrm{H}_{2}\right)$ gets oxidised to water $\left(\mathrm{H}_{2} \mathrm{O}\right)$.
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