4FeO + O2 = 2Fe2O3 is a redox reaction where Fe is oxidized and O is reduced. FeO is a reducing agent (i.e. it lost electrons) and O 2 is a oxidizing agent (i.e. it gained electrons). Balance Using Half-Reaction (aka Ion-Electron) Method. Balance Using Oxidation Number Change Method. Balance Using Aggregate Redox Species (ARS) Method.