Comment on each of the given observations : Lithium is the only alkali metal to form a nitride directly.

Explanation

The lattice energy of lithium nitride (Li,N) which consists of a small cation `(Li^(+))` and a small anion `(N^(3-))` is much higher and this energy compensates for the high bond dissociation energy of `N -=N` bond and the energy to form `N^(3-)` ion. Larger alkali metal requirements. Hence, Li is the only alkali metal which forms nitride directdy.