In white phosphorus (P₄), each phosphorus atom is bonded to three other phosphorus atoms in a tetrahedral structure, exhibiting a single P-P bond. To determine the oxidation number of phosphorus, we consider that the overall charge of the molecule is neutral. Since there are four phosphorus atoms in the P₄ molecule, the sum of their oxidation numbers should be zero. Each P-P bond contributes two shared electrons, meaning each phosphorus atom shares one valence electron with each of the other three phosphorus atoms. Therefore, each phosphorus atom has three shared electron pairs, resulting in a formal charge of 0.