Why are `BeSO_(4)` and `MgSO_(4)` readily soluble in water while `CaSO_(4),SrSO_(4)` and `BaSO_(4)` are insoluble?

Explanation

The hydration enthalpies of `BeSO_(4) and MgSO_(4)` are quite high because of small size of `Be^(2+) and Mg^(2+)` ions. These hydration enthalpy values are higher than their corresponding lattice enthalpies and therefore, `BeSO_4` and `MgSO_(4)` are highly soluble in water. However, hydration enthalpies of `CaSO_4, SrSO_4 and BaSO_(4)` are not very high as compared to lattice enthalpies and hence these are insoluble in water.