Question

In an aqueous electrolytic cell, nitrate ions never react at the anode, but nitrite ions do. Explain.

Short answer

Unlike nitrites, nitrates can no longer be oxidised.

Step-by-step solution

Step 1:

In nitrates, the oxidation number of Nitrogen is $\mathbf{+}\mathbf{5}$, while in nitrites, the oxidation number of Nitrogen is only$\mathbf{+}\mathbf{3}$,therefore it can still be further oxidized and have its oxidation number increase.

Nitrates do not react in the anode because they can no longer be oxidized, unlike nitrites. Hence nitrate can no Longer be oxidized, unlike nitrites.