JEE Main · 2024 · 27 Jan 2024 · Shift 2 · Redox Reactions and Electrochemistry

A species can act as an oxidising agent only if it can itself be reduced, i.e. its central atom must be able to drop to a lower oxidation state. In $N^{3-}$, nitrogen is already at its lowest possible oxidation state $(-3)$, so it cannot accept any more electrons and cannot function as an oxidising agent — it can only be oxidised.

In $S{O}_4^{2-}$ sulfur is $+6$, in $Br{O}_3^{-}$ bromine is $+5$, and in $Mn{O}_4^{-}$ manganese is $+7$ — all three can be reduced to lower oxidation states and so all act as oxidising agents.