 For an atom in its elemental state, the oxidation number is:  For any monatomic ion, the oxidation number equals:  The oxidation number of oxygen is usually:  The major exception is in peroxides (containing the O 2 2- ion)  The oxidation state of Hydrogen is:  The oxidation number of Flourine is:  The sum of oxidation numbers in polyatomic a polyatomic ion: 