Final answer:
The phosphite group is represented by the chemical formula PO33-, which differs from the phosphate group by having one less oxygen atom and phosphorus in a +3 oxidation state.
Step-by-step explanation:
The phosphite group is different from the phosphate group, which you've correctly identified as PO43-. While the phosphate ion contains phosphorus in a +5 oxidation state, the phosphite ion contains phosphorus in a lower oxidation state of +3. The chemical formula for the phosphite ion is PO33-, where one less oxygen atom is bonded to the phosphorus atom compared to phosphate.
This difference in oxidation states and the number of oxygen atoms leads to different properties and reactivity for these ions. Phosphite ions are also important in various chemical reactions and biological systems but are less oxidized than phosphate ions.