Nitrogen exists as diatomic molecule and phosphorous acts as tetra atomic molecule. Explain.

Explanation

Due to smaller atomic size of N, `p pi-p pi` bonding in nitrogen is possible. A such nitrogen exists as triply bonded discrete diatomic molecule `(N -= N)` and due to lesser molecular mass, is a gas at room temperature. On the other hand, atomic size of phosphorus is much larger than nitrogen. As such `p pi-p pi` bonding in phosphorus is not possible and it exist as pyramidal tetratomic molecule `(P_4)` in which each P atom is bonded to three other P atoms by three sigma bonds. Due to larger molecular mass of molecule, phosphorus is a solid at room temperature.