Here's why:
* Oxidation state represents the charge an atom would have if all its bonds were completely ionic.
* In elemental oxygen (O₂), the two oxygen atoms are bonded to each other by a double bond.
* Since they are the same element, they have equal electronegativity, meaning the electrons are shared equally.
* Therefore, there is no transfer of electrons, and each oxygen atom has a formal charge of 0.
