The oxidation number of P4 is 0.
To understand why, let’s break it down. Phosphorus in its elemental form, like P4, is composed of phosphorus atoms bonded together. In chemical terms, the oxidation number reflects the degree of oxidation of an atom in a compound. When atoms are in their elemental form, they do not exhibit any charge or oxidation state; hence, their oxidation number is set to zero.
In P4, all four phosphorus atoms are identical and share electrons equally, so there’s no loss or gain of electrons for any of the atoms. Therefore, the overall oxidation number for all the phosphorus atoms in the molecule remains at 0. This is a fundamental concept in oxidation states and helps to determine how elements interact in various chemical reactions.