What is the formula for phosphite?

Phosphite is an anion derived from phosphorous acid (H3PO3), and its formula is represented as PO3 with a charge of 3-. This is because phosphite consists of one phosphorus atom and three oxygen atoms, and the entity bears a negative charge of three.

The other options represent different chemical species. The formula PO4(3-) indicates phosphate, which contains an additional oxygen atom compared to phosphite. S2O3(2-) represents thiosulfate, a different anion composed of sulfur and oxygen. MnO4(-) is the permanganate ion, another distinct anion consisting of manganese and oxygen. Thus, the unique composition of PO3(3-) makes it the correct representation for phosphite, confirming that it is the only option expressing this specific chemical species.