Nitrogen exists as diatomic molecule and phosphorus as `P_(4)`. Why?

Explanation

Nitrogen forms `ppi-ppi` multiple bonds owing to its small size and high electronegativity.
Therefore it exists as a diatomic molecule, with a triple bond between two nitrogen atoms. However, the larger size and low electronegativity of P-atom does not promote the `ppi-ppi` multiple bonds between the P-atoms. Instead, it forms P-P single bonds and exists as tetra-atomic `(P_(4))` molecule.