JEE Main · 2016 · 03 Apr 2016 · Offline · Chemical Bonding and Molecular Structure

Hybridisation follows from the number of sigma bonds and lone pairs on nitrogen. In $\mathrm{NO}{}_2{}^{+}$ the nitrogen is doubly bonded to each oxygen with no lone pair, $\mathrm{O}=\mathrm{N}{}^{+}=\mathrm{O}$, so two electron domains give a linear shape and $sp$ hybridisation. In $\mathrm{NO}{}_2{}^{-}$, $\mathrm{NO}{}_3{}^{-}$ and $\mathrm{NO}{}_2$ a lone pair or extra domain makes the nitrogen $s{p}^2$. The species with $sp$ nitrogen is $\mathrm{NO}{}_2{}^{+}$.