The given complex is [X(NH3)5SO4]Cl Corodination number maybe defined as the number of coordinate bonds formed with the central metal atom / ion by the ligands Here six ligands (5 - NH3 and on SO42−) are coordinated to the central metal X. So, the coordination number is 6. The oxidation number of the central atom is defined as the charge that it carries as calculated by assigning appropriate charges on the central atom and the ligands equal to the charge on the coordination sphere. Suppose the charge carries by X is q i.e., q + 5 × 0 - 2 - 1 = 0 q = + 3 Oxidation number is 3