Give reason(s) why elemental nitrogen exists as a diatomic molecular whereas elemental phosphorus as a tetraatomic molecule.

Elemental nitrogen exists-as a diatomic molecule because nitrogen can form pπ – pπ multiple bonds which is not possible in case of phosphorus due to repulsion between, non-bonded electrons of the inner core. There is no such repulsion in case of smaller nitrogen atoms as they have only Is² electrons in their inner core.