JEE Main · 2026 · 24 Jan 2026 · Shift 2 · Chemical Bonding and Molecular Structure

Using molecular-orbital filling, count electrons and bond order for each species. $O_2^{+}$ has $15$ electrons, bond order $\frac{10-5}{2}=2.5$ with one unpaired electron, so it is paramagnetic. $N_2^{-}$ also has $15$ electrons, bond order $\frac{10-5}{2}=2.5$ with one unpaired electron, so it too is paramagnetic. By contrast $O_2^{-}$ has bond order $1.5$ and $N_2^{2-}$ has bond order $2$, so neither matches $O_2^{+}$. The pair with the same bond order $2.5$ that are both paramagnetic is $O_2^{+}$ and $N_2^{-}$.