Which of the following represents the phosphate ion?

The phosphate ion is represented by the formula PO4^3-. This indicates that the ion consists of one phosphorus atom bonded to four oxygen atoms and carries a -3 charge. The structure reflects the typical form of the phosphate ion found in various biological and chemical processes, including its role in energy transfer (as found in ATP) and its presence in nucleic acids.

The other options represent different chemical species related to phosphate but do not denote the simplest or most common form of the phosphate ion. For example, HPO4^2- is the hydrogen phosphate ion, which has one less negative charge than the phosphate ion and includes a hydrogen ion. Similarly, H2PO4- is the dihydrogen phosphate ion, which carries a -1 charge and contains two hydrogen atoms attached to the phosphate structure. PO3^3-, while it might seem like a valid option for phosphorus and oxygen, is not the conventional representation of the phosphate ion due to its different stoichiometry.

Therefore, the most accurate representation of the phosphate ion is indeed PO4^3-.