Explanation

(c)
The solubility of sulphates of alkaline earth metals decreases regularly on moving down the group because solubility product decreases from $BeSO_{4}\ to\ BaSO_{4}.$ Hence, the order of solubility of their sulphates is
$BeSO_{4}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ > MgSO_{4}\ \ \ > CaSO_{4}\ \ \ \ \ \ \ \ > SrSO_{4}\ \ \ \ \ \ \ \ \ \ > BaSO_{4}$
$K_{sp}\ :very\ high\ \ \ \ \ \ \ \ \ \ 10\ \ \ \ \ \ \ \ \ \ \ \ \ 2.4 \times 10^{- 5}\ \ \ \ \ \ \ \ 7.6 \times 10^{- 7}\ \ \ \ \ \ \ 1.5 \times 10^{- 9}$