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Q.
Nitrogen forms $N_{2}$ , but phosphorus is converted into $P_{4}$ from $P$, the reason is
NTA AbhyasNTA Abhyas 2020The p-Block Elements - Part2
Solution:
Nitrogen form $N _{2}$ (i.e. $N \equiv N$ ) but phosphorus form $P _{4}$, because in $P _{2}$,
$p \pi - p \pi$ bonding is present which is a weaker bonding.
Nitrogen is smaller in size hence it forms multiple bond with other nitrogen atom $( N \equiv N )$
Nitrogen has unique ability to form $p \pi - p \pi$ multiple bonds with itself and with other elements having small size and high electron negativity.
However heavier elements of this group do not form $p \pi - p \pi$ bonds as their atomic orbitals are so large and diffuse that they cannot have effective overlapping.
Thus nitrogen exist as diatomic molecule with a triple bonds.
The single $P$ - $P$ bond is stronger and has higher catenation tendency