Answer
a) $AgCl$
b) $Ca(OH)_2$
c) $Ca(OH)_2$
Work Step by Step
a) $Ksp=[Ag^+][Cl^-]=s^2$, $Ksp=[Ag^+][CN^-]=s^2$
AgCl is more soluble in water because it has a higher Ksp
b) $Ksp=[Mg^{2+}][OH^-]^2=s\dot{}(2s)^2=4s^3$,
$Ksp=[Ca^{2+}][OH^-]^2=s\dot{}(2s)^2=4s^3$
$Ca(OH)_2$ is more soluble in water because it has a higher Ksp
c) $Ksp=[Ca^{2+}][OH^-]^2=s\dot{}(2s)^2=4s^3\rightarrow s=0.024\ M$,
$Ksp=[Ca^{2+}][SO_4^{2-}]=s^2\rightarrow s=0.007\ M$
$Ca(OH)_2$ has a higher solubility in water.
