For example:

* In H₂O, the oxidation number of hydrogen is +1, so it would be written as H⁺¹.

* In CO₂, the oxidation number of carbon is +4, so it would be written as C⁺⁴.

Important Notes:

* The oxidation number is not a true charge on an atom, but rather a bookkeeping device used to track electron transfer in chemical reactions.

* The oxidation number of an element in its elemental form is always zero.

* The sum of the oxidation numbers of all atoms in a neutral molecule must be zero.

* The sum of the oxidation numbers of all atoms in a polyatomic ion must equal the charge of the ion.