Potassium cyanide is used for separating

Question

(a) $Co^{2+}$ and $Ni^{2+}$
(b) $Mn^{2+}$ and $Zn^{2+}$
(c) $Ba^{2+}$ and $Ca^{2+}$
(d) $Ca^{2+}$ and $Cd^{2+}$