How can oxidation numbers identify which atoms are oxidized and reduced?

In an oxidation-reduction reaction, atoms are assigned an oxidation number to track the movement of electrons during bond formation. These numbers allow chemists to identify which species are oxidized or reduced by observing changes in the oxidation state from the reactants to the products.12

The identification process follows these rules:

• Oxidation: An atom is oxidized if its oxidation number increases during the reaction. This corresponds to the loss of electrons.13
• Reduction: An atom is reduced if its oxidation number decreases during the reaction. This corresponds to the gain of electrons.13

For example, if an element's oxidation state shifts from 0 to +2, it has been oxidized because its oxidation number increased. Conversely, if an element shifts from +3 to +2, it has been reduced because its oxidation number decreased. This system provides a consistent way to analyze redox processes as electron-transfer reactions, even when oxygen or hydrogen atoms are not directly involved.413