(a) Both Li+ and H- have small size and their combination has high lattice energy. Therefore, LiH is stable as compared to NaH.
(b) Alkali metals have only one electron per metal atom. As a result, the binding energy of alkali metal ion in the close-packed metal lattices is weak. Therefore, these are soft and have low melting point.
(c) Alkaline earth metals form di-positive ions in their salts. These di-positive ions have noble gas configurations with no unpaired electrons. Therefore, these compounds are colourless and diamagnetic.
