By applying the various rules for determining the oxidation number of different atoms in a compound, the oxidation number of each metallic element in the given compounds is as follows:
In HAuCl2 , Au has +3; in Ti2O, Ti has +1; in FeO, Fe has +2; in Fe2O2 , Fe has +3; in Cul, Cu has +1 : in CuO, Cu has +2; in MnO, Mn has +2 while in Mn2O , Mn has +4 oxidation state. Therefore, these compounds may be represent as :
HAu(II)Cl4, Ti2(I)O, Fe(II)O, Fe2(III)O3, Cu(I)I, Cu(II)O, Mn(II)O, and Mn(IV)O2.
