`LiH overset(Delta)toxx" but " 2NaH overset(Delta)to 2Na + H_2uarr` Explain the above observations.

Explanation

The smaller `Li^(+)` ion exerts a strong polarising power on highly polarisable `H^(-)` ion and as a result, the two atoms remain strongly attached by a covalent bond. On the other hand, due to low polarising power of `Na^(+)` ion, NaH is essentially ionic & so it dissociates on heating to yield metallic sodium and dihydrogen.