The correct order of the solubility of alkaline-earth metal sulphates in water is:

Step-by-step solution

Hydration power energy ∝ q 1 q 2 ( 1 r + + 1 r − ) ∴ Solubility order of IIA group element sulphates in water: M g S O 4 > C a S O 4 > S r S O 4 > B a S O 4 Generally bigger size ion form a strong bond with bigger ion so solubility will decrease or smaller the cation, greater the hydration sphere. Hence, Solubility of SO 4 - 2 ion with alkali or alkaline earth metal decrease top to bottom.