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

Options

A. `Mg gt Ca gt Sr gt Ba`
B. `Ca gt Sr gt Ba gt Mg`
C. `Sr gt Ca gt Mg gt Ba`
D. `Ba gt Mg gt Sr gt Ca`

Answer

A

Explanation

Solubility of the sulphates The sulphates becomes less soluble as you go down the group i.e. Mg gt Ca gt Sr gt Ba
The magnitude of the lattice energy remains almost constant as the size of the sulphate ion is so big that small increase in the size of the sulphate ion is so big that small increase in the size of the cation from Be to Ba does not make any difference However, the hydration energy decreases from `Be^(2+)` to `Ba^(2+)` appreciably as the size of the cation increases down the group. The significantly high solubility of `MgSO_4` is due to high enthalpy of solvation of the smaller `Mg^(2+)` ions.