A-Level chem- lattice energy problem

The solubility of sulphates(VI) decreases down Group II

Explanation : ΔHsolution = energy needed to break the lattice - energy released in hydration
The more exothermic the ΔHsolution, the higher the solubility.
Sulphate(VI) ion, SO42-, is large in size. For the sulphate(VI) of a Group II metal, the cation is much smaller than the SO42- cation. Down Group II, the increase in cationic size does not cause a significant change of lattice enthalpy, but causes less energy to be released in hydration. Consequently, the values of ΔHsolution of their sulphates(VI) down Group II become less exothermic (or even more endothermic).