JEE Main · 2019 · 10 Apr 2019 · Shift 1 · Atomic Structure

Isoelectronic species carry the same number of electrons. Counting through the sets, the one in which every member has $10$ electrons is $\mathrm{N}{}^{3-}$, $\mathrm{O}{}^{2-}$, $\mathrm{F}{}^{-}$ and $\mathrm{Na}{}^{+}$. The other groupings each include a two-electron species such as $\mathrm{Li}{}^{+}$, which breaks the match, so the nitride-oxide-fluoride-sodium set is the isoelectronic one.