What is the oxidation number of an element in its elemental form?

The oxidation number of an element in its elemental form is zero. This is because oxidation states are used to indicate the degree of oxidation (loss of electrons) of an element in a compound or reaction. In elemental form, an atom does not gain or lose electrons; it is in its most stable, neutral state. Therefore, elements like O2, N2, H2, and any other pure elements such as gold (Au) or silver (Ag) all have an oxidation number of zero. This fundamental principle applies universally across all elements regardless of their specific properties, making it a key concept in understanding redox reactions and the behavior of elements in compounds.