The solubility of the alkaline earth's metal sulphates in water decreases in the sequence:

Step-by-step solution

The lattice energies of alkaline earth sulphates are almost constant, but Hydration   energy ∝ 1 S i z e   o f   c a t i o n For M g 2 + → C a 2 + → S r 2 + → B a 2 + , the cationic size increases, so the hydration energy decreases, i.e. M g S O 4 is soluble and B a S O 4 is a precipitate. M g S O 4 > C a S O 4 > S r S O 4 > B a S O 4