5The algebraic sum of the oxidation numbers in a neutral compound must be zero;in a polyatomic ion, the sum must be equal to the ion charge. Example: H.IO Theoxidationnumberof Iis+7 S2 Theoxidationnumberof Sis+2 TheoxidationnumberofSis+2.5 8 Fe;O The oxidation number of Feis+ 3 DExample： ⑤The algebraic sum of the oxidation numbers in a neutral compound must be zero; in a polyatomic ion, the sum must be equal to the ion charge. H5 I O6 Theoxidation number o f Iis +7 3 8 Fe O The oxidation number of Fe is 3 4 + S O Theoxidation number o f Sis 2.5 2 4 6 +  S O Theoxidation number o f Sis 2 2 2 3 + 