The correct order of solubility of the sulphates of alkaline earth metals in water is

Options

A. `BegtCagtMggtBagtSr`
B. `MggtBegtBagtCagtSr`
C. `BegtMggtCagtSrgtBa`
D. `MggtCagtBagtBegtSr`

Answer

C

Explanation

The solubility of the sulphates in water decreases down the group i.e.
`BegtMggtCagtSrgtBa`
Thus `BeSO_(4) and MgSO_(4)` are highly soluble `CaSO_(4)` is sparingly soluble but the sulphates of Sr, Ba and Ra are virtually insoluble.
Reason : The magnitude of the lattice energy remains almost constant as the sulphate 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. Hence the solubilities of sulphates of alkaline earth metals decrease down the group mainly due to the decreasing hydration energies from `Be^(+2)" to "Ba^(+2)`. The high solubility of `BeSO_(4)andMgSO_(4)` is due to high hydration energies due to smaller `Be^(+2)andMg^(+2)` ion.