Nitrogen has five valence electrons. To satisfy the octet rule, it needs three more electrons. In ammonia (NH3), nitrogen forms three covalent bonds with three hydrogen atoms, each contributing one electron. This gives nitrogen a total of eight electrons, satisfying the octet rule.

In order to form pentahydride of nitrogen (NH5), nitrogen would have to form five covalent bonds with five hydrogen atoms. However, this is not possible because nitrogen only has five valence electrons. Even if nitrogen could form five covalent bonds, the molecule would be highly unstable due to the high number of electron pairs around the nitrogen atom.

Therefore, pentahydride of nitrogen is not possible.