Among the given group-15 elements, nitrogen can form multiple bonds with itself. A strong multiple bonds are formed only when the overlapping is effective. i.e. overlapping orbitals are of similar energy and same symmetry. Nitrogen has small size and has 2p orbitals (lower energy), shows pπ−pπ bonding. Whereas, in the heavier elements the overlapping orbitals are bigger and are very high in energy as atomic size increases down the group. Thus, in these cases, effective overlapping for pπ−pπ bond, does not takes place.