What is the common name for P2O3?

The common name for P2O3 is diphosphorus trioxide. This name is derived from the IUPAC nomenclature system, which emphasizes the number of phosphorus atoms and oxygen atoms in the compound. In P2O3, there are two phosphorus atoms, indicated by the prefix "di-," and three oxygen atoms, which corresponds to the "tri-" prefix. Therefore, combining these prefixes with the elemental names gives us the name diphosphorus trioxide.

This is the standard way to name binary compounds where both elements are nonmetals. The other choices do not accurately reflect the composition of P2O3. For example, phosphorus oxide is a general term that could refer to various phosphorus-oxygen compounds without specifying the number of each element present. Triphosphorus trioxide would imply there are three phosphorus atoms, which does not match the formula. Phosphoric acid is a specific acid with a different chemical formula (H3PO4) and does not relate to P2O3. Thus, the correct choice clearly outlines the specific composition of the compound.