Which species acts as the reducing agent in the reaction $3\text{Cu}+8{\text{HNO}}_3\to 3\text{Cu}({\text{NO}}_3{)}_2+2\text{NO}+4{\text{H}}_2\text{O}$?

Solution

1. Assign oxidation states: $\text{Cu}$ is $0$ on the left and $+2$ in $\text{Cu}({\text{NO}}_3{)}_2$ on the right.
2. Since the oxidation state of $\text{Cu}$ increases from $0$ to $+2$, it is oxidized.
3. The species that is oxidized acts as the reducing agent.
4. Therefore, $\text{Cu}$ is the reducing agent.
5. Hence the answer is (A).