(a) Why does the solubility of alkaline earth metal hydroxides in water increase down the group.
(b). Why does the solubility of alkaline earth metal carbonates and sulphates in water decrease doewn the group?

Explanation

a. Among alkaline earth metal hydroxides, the anion being common, the cationic radius will influence the lattice enthalpy.Since lattice enthalpy decreases much more than the hydration enthalpy with increasing ionic size, the solubility increases down the group `(darr)`.
b. The size of anions being much larger as compared to cations, the lattice enthalpy will remain almost constant within a particular group. Since the hydration enthalpy decreases down the group, solubility will decreases as found for alkaline earth metal carbonates and sulphates.