Which ion is known as phosphate?

Phosphate is primarily recognized as the ion represented by the formula PO4 3-. This polyatomic ion consists of one phosphorus atom bonded to four oxygen atoms, carrying a total charge of minus three. In biological systems, phosphate plays a crucial role in many processes, including energy transfer (as seen in ATP), as well as in the formation of nucleic acids and phospholipids, which are fundamental components of cell membranes.

The other chemical species provided in the choices represent different ions. HPO4 2- is known as hydrogen phosphate and is a different species from the fully deprotonated phosphates. NO2- is the nitrite ion, and SO4 2- is sulfate. Each of these ions has distinct structures and functions that do not relate to the phosphate category. Therefore, PO4 3- is unequivocally identified as phosphate due to its specific composition and characteristic properties.