WAEC Chemistry 2019 Paper

Concept:A reducing agent is a substance that donates electrons and gets oxidized in a reaction.Explanation:In the reaction, $2\mathrm{NH}_3 + 3\mathrm{Cl}_2 \rightarrow \mathrm{N}_2 + 6\mathrm{HCl}$, the oxidation state of nitrogen changes from $-3$ in $\mathrm{NH}_3$ to $0$ in $\mathrm{N}_2$.This means nitrogen is oxidized, as its oxidation number increases.Meanwhile, chlorine is reduced from $0$ in $\mathrm{Cl}_2$ to $-1$ in $\mathrm{HCl}$.Because ammonia causes chlorine to be reduced while itself being oxidized, ammonia acts as a reducing agent.Answer:A. a reducing agent