What is the oxidation number of CO?

Carbon monoxide is a neutral molecule; the oxidation number or state of carbon is +2 and oxygen is -2. The two possible oxidation numbers for oxygen are -1 and -2; the oxidation state -1 occurs in peroxides and is fairly uncommon, so the oxidation state of oxygen is -2.

Because carbon monoxide is a neutral molecule, the oxidation state of carbon must be +2. The oxidation state of an atom refers to processes involving a loss of electrons, so the oxidation number on an ion is the hypothetical charge that an ion would have in a compound that consists entirely of ionic bonds.