Answer
See explanation below.
Work Step by Step
a.II shows +2 oxidation state. As there are 6 water molecules bonded to Ni and each ligand is unidentate, so the coordination number is 6.
b.III shows +3 oxidation state.As 3 ethylenediamine molecules are bonded to Cr, but each ethylenediamine molecule contains two donor N atoms (bidentate). So, the coordination number is 6.
c.II shows +2 oxidation state.As there are 6 unidentate cyano molecules bonded to Mn, so the coordination number is 6
