JEE Main · 2019 · 09 Jan 2019 · Shift 2 · Chemical Bonding and Molecular Structure

We want a step where the bond order rises and an unpaired-electron (paramagnetic) species becomes fully paired (diamagnetic). Take $\mathrm{NO}\to \mathrm{NO}{}^{+}$: neutral $\mathrm{NO}$ has $15$ electrons, bond order $2.5$, and one unpaired electron, so it is paramagnetic. Removing that lone antibonding electron gives $\mathrm{NO}{}^{+}$ with $14$ electrons, bond order $3$, and all electrons paired -- diamagnetic. Bond order has gone up and the paramagnetism is gone, which the $\mathrm{N}{}_2\to \mathrm{N}{}_2{}^{+}$, $\mathrm{O}{}_2\to \mathrm{O}{}_2{}^{+}$ and $\mathrm{O}{}_2\to \mathrm{O}{}_2{}^{2-}$ changes do not achieve.