Nitrogen exists as a diatomic molecule $(N_2)$ and phosphorus as $P_4$. Why?

(N/A) Nitrogen,due to its small size and high electronegativity,has a strong tendency to form $p\pi-p\pi$ multiple bonds with itself. This results in the formation of a stable diatomic molecule,$N_2$,held together by a triple bond.
As we move down the group,the atomic size increases,which makes the effective overlapping of $p$-orbitals for $p\pi-p\pi$ bonding difficult.
Consequently,heavier elements like phosphorus prefer to form single bonds with three other atoms,leading to the formation of a tetrahedral $P_4$ molecule.