Oxygen in peroxides: Peroxides include hydrogen peroxide, H2O2. This is an electrically neutral compound, so the sum of the oxidation states of the hydrogen and oxygen must be zero. Because each hydrogen has an oxidation state of +1, each oxygen must have an oxidation state of -1 to balance it.

+4

Vanadium(IV) oxide or vanadium dioxide is an inorganic compound with the formula VO2. It is a dark blue solid. Vanadium(IV) dioxide is amphoteric, dissolving in non-oxidising acids to give the blue vanadyl ion, [VO]2+ and in alkali to give the brown [V4O9]2− ion, or at high pH [VO4]4−.

Though it is very reactive, the oxidation number of ozone (O3​) is zero: it is the tri-atomic form of elemental oxygen. The same applies to the di-atomic O2​ molecule.

+2

+1

The Chemistry of Phosphorus

+5

In compounds of phosphorus (where known), the most common oxidation numbers of phosphorus are: 5, 3, and -3.

+3

Oxidation number means that the number of electrons either lost or gained by an atom of an element during compound formation. However for Chlorine gas, the oxidation number (Cl2) is zero.

The above table can be used to conclude that boron (a Group III element) will typically have an oxidation state of +3, and nitrogen (a group V element) an oxidation state of -3.