When using this method for the reaction of C to CO 2 , the C in carbon dioxide has an oxidation number of 4+ while the two oxygens have an oxidation number of 2- . Clearly, the C has "lost electrons" ...When using this method for the reaction of C to CO 2 , the C in carbon dioxide has an oxidation number of 4+ while the two oxygens have an oxidation number of 2- . Clearly, the C has "lost electrons" and has become oxidized by interacting with the oxidizing agent O 2 . as it went from C to CO 2 . If the atoms connected by a bond are identical, we split the electrons and assign one to each atom.