Among $Ba X^{2 +}$ , $Sr X^{2 +}$ and $Ca X^{2 +}$ (as separate dilute solutions), the one that gives no precipitate with freshly prepared saturated $CaSO X_{4}$ solution is

Answer: D

The sulphates become less soluble down the group:

BaSO X_{4}

forms at once and

SrSO X_{4}

slowly on standing, but a saturated solution of

CaSO X_{4}

already holds the maximum

SO X_{4} X^{2 -}

that

CaSO X_{4}

can allow, so

Ca X^{2 +}

gives nothing.