In a redox reaction, one of the reactants loses electrons, while the other gains electrons. Electrons are negatively charged subatomic particles that orbit around positively charged atomic nuclei. Oxidation is the loss of electrons by an atom or molecule, resulting in an increase in its oxidation state. Reduction is the gain of electrons by an atom or molecule, resulting in a decrease in its oxidation state. If a molecule or atom is oxidized, it is a reducing agent because it has lost electrons that it can transfer to another molecule. If a molecule or atom is reduced, it is an oxidizing agent because it has gained electrons that it can transfer to another molecule.