The correct order of the solubility of alkaline-earth metal...

Hydration power energy $∝$ ${\text{q}}_{\text{1}} {\text{q}}_{\text{2}} ( \dfrac{\text{1}}{{\text{r}}_{+}} \text{+}\dfrac{\text{1}}{{\text{r}}_{-}} )$

$∴$ Solubility order of IIA group element sulphates in water:

$MgS{O}_{4} > CaS{O}_{4} > SrS{O}_{4} > BaS{O}_{4}$

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.