Because of big size of `SO_(4)^(2-)` ion as compared to `Be^(2+)` and `Mg^(2+)` ions , the lattice enthalpies of `BeSO_(4)` and `MgSO_(4)` are almost the same . But because of small size of `Be^(2+)` and `Mg^(2+)` ions their hydration enthalpies are much higher than their corresponding lattice enthalpies . As a result , `BeSO_(4)` and `MgSO_(4)` are highly soluble in water .
