Explain the "Oxidation" in terms of gain or loss of oxygen with two examples.

(N/A) Oxidation is defined as the gain of oxygen by a substance during a chemical reaction.
For example:
$(i)$ $H_2 + CO_2 \rightarrow H_2O + CO$
In this reaction, $H_2$ gains oxygen to form $H_2O$, therefore $H_2$ is oxidized.
$(ii)$ $2Cu + O_2 \rightarrow 2CuO$
In this reaction, $Cu$ gains oxygen to form $CuO$, therefore $Cu$ is oxidized.