Answer
a) $ CaSO_{4}(s) \leftrightharpoons Ca^{2+}(aq) + SO_{4}^{2-}(aq) $
$K_{sp} = [Ca^{2+}][SO_{4}^{2-}] $
b) $ AgCl(s) \leftrightharpoons Ag^{+}(aq) + Cl^{-}(aq)$
$K_{sp} = [Ag^{+}][Cl^{-}]$
c) $ CuS(s) \leftrightharpoons Cu^{2+}(aq) + S^{2-}(aq)$
$K_{sp} = [Cu^{2+}][S^{2-}]$
d) $ FeCO_{3}(s) \leftrightharpoons Fe^{2+}(aq) + CO_{3}^{2-}(aq) $
$K_{sp} = [Fe^{2+}][CO_{3}^{2-}]$
Work Step by Step
Let's say, we have to find equation of a compound AB showing how the compound dissolve in water.
Let's say both A and B have vacancies$ = x$
Then, the equilibrium equation that shows how the compound dissolves in water is as follows:
$AB(s) \leftrightharpoons A^{x+}(aq) + B^{x-} (aq)$
$ \therefore K_{sp} = [A^{x+}][B^{x-}]$
N. B. As the compound is solid, the equilibrium concentration of AB will be unity. $\therefore [AB] = 1$
