Give reasons for the following:
Dinitrogen is a gas but phosphorus is a solid.

Explanation

Due to small size and high electronegativity, nitrogen froms `p pi- p pi ` bonds and exists as diatomic molecules. These molecules are held together by weak van der Waals forces and hence `N_2` exists as a gas at room temperature. In contrast, due to large size and lower electronegativity, P does not form `p pi- p pi ` bond with itself. Rather it prefers to form single P-P bonds and exists as a `P_4` molecule. Due to bigger size, attractions holding `P_4` molecules are quite strong. Thus P is a solid at room temperature.