Nitrogen exists as diatomic molecule and phosphorus as P4. Why?
Nitrogen exists as diatomic molecule and phosphorus as P4. Why?

Nitrogen because of its small size has a capacity to form  multiple bonds with itself.
Thus, nitrogen forms a very stable diatomic molecule, N2​. On moving down a group, the tendency to form  bonds decreases (because of an increase in the size of heavier elements down the group). Therefore, phosphorus (like other heavier metals) exists in the P4​ state and not in the P2 state.