Arrange the following sulphates of alkaline earth metals in order of decreasing thermal stability: `BeSO_(4),MgSO_(4),CaSO_(4),SrSO_(4)`.

Explanation

Sulphate decompose on heating to give the corresponding oxide.
`MgSO_(4)overset(Delta)(rarr)MgO+SO_(2)+(1)/(2)O_(2)`
The stability increases as the electropositive character of the metal or basic nature of the metal increases down the group `(darr)`. This is clear form the increasing decomposition temperature down the group.
`1647 K 1422 K 1168 K773 Krarr` Temperature of decomposition
`SrSO_(4) gt CaSO_(4) gt MgSO_(4) gt BeSO_(4)`