Which element in the reaction $2\text{Na}+{\text{Cl}}_2\to 2\text{NaCl}$ undergoes oxidation?

Solution

1. Assign oxidation states: $\text{Na}$ is $0$ and ${\text{Cl}}_2$ is $0$.
2. In $\text{NaCl}$, $\text{Na}$ is $+1$ and $\text{Cl}$ is $-1$.
3. Sodium increases from $0$ to $+1$, which is oxidation.
4. Chlorine decreases from $0$ to $-1$, which is reduction.
5. Hence the answer is (A).