JEE Main 2025 Jan 22 Shift 2, Chemistry Q3: Valence Bond Theory And Hybridisation

Among non-metals of group 15, the single-bond strength order is $N-N<P-P$. The $N-N$ bond is unusually weak because the small size of nitrogen brings the two lone pairs close enough to cause significant lone pair$-$lone pair repulsion.

So the element with the weakest E$-$E single bond is nitrogen.

Nitrogen lacks accessible d-orbitals in its valence shell (only $2s$ and $2p$ available), so it cannot expand its octet. Its maximum covalency is therefore limited to 4 (as seen in $N{H}_4^{+}$).

$\therefore$ Maximum covalency $=4$.