Compare the alkali metals and alkaline earth metals with respect to (a) ionisation enthalpy, (b) basicity of oxides and (c) solubility of hydroxides.

Explanation

(i) Ionisation enthalpy. Ionisation enthalpies of alkaline earth metals are higher than those of alkali metals. This is because of smaller size of alkaline earth metal corresponding to alkali metal of the same period. (ii) The oxides of alkali and alkaline earth metals dissolve in water to form their respective hydroxides. These oxides are strong bases. However, the oxides of alkali metals are more basic than those of alkaline earth metals. This is because the ionization enthalpy of alkali metals is lower or the electropositive character of alkali metals is higher than that of corresponding alkaline earth metal so that M-OH bond in alkali metals can more easily ionize.
`MOH to M^(+) + OH^(-)`
(iii) Because of small size and high charge, the lattice enthalpies of alkaline earth metals are much more than those of alkali metals and therefore, the solubility of alkaline earth metal hydroxides is less
than that of alkali metals.