An aqueous solution of metal ion M1 reacts separately with reagents Q and R in excess to give tetrahedral and square planar complexes, respectively. An aqueous solution of another metal ion M2 always forms tetrahedral complexes with these reagents. Aqueous solution of M2 on reaction with reagent S gives a white precipitate which dissolves
in excess of S. The reactions are summarized in the scheme given below.
M1, Q, and R, respectively, are:
1. \(Zn^{2+}, ~ KCN\) and \(HCl\)
2. \(Ni^{2+},~ HCl\) and \(KCN\)
3. \(Cd^{2+}, ~KCN\) and \(HCl\)
4. \(Co^{2+},~ HCl\) and \(KCN\)