The n-factor, or the oxidation state change number, of a molecule or ion represents the number of electrons transferred during a redox (reduction-oxidation) reaction. In the case of O2 (oxygen gas), it is a molecule consisting of two oxygen atoms bonded together.
Oxygen gas, O2, is a neutral molecule where each oxygen atom has an oxidation state of 0. In this case, there is no transfer of electrons within the molecule itself, so the n-factor for O2 is 0.
However, it's worth noting that during chemical reactions, O2 can participate as an oxidizing agent, accepting electrons from other species and getting reduced itself. In such cases, the n-factor for O2 would depend on the specific reaction and the change in oxidation state of oxygen as it gains electrons.