Chemistry Regents Practice Test

Which of the following statements about the phosphate ion is true?

1. It possesses a +3 charge

2. It possesses a -2 charge

3. It possesses a -3 charge

4. It is a neutral ion

The correct answer is: It possesses a -3 charge

The phosphate ion is represented chemically as \( \text{PO}_4^{3-} \). It carries a formal charge of -3 due to the presence of four oxygen atoms, each contributing a -2 oxidation state, and one phosphorus atom with a +5 oxidation state. When adding the oxidation states of the constituent atoms, the result indicates that the overall charge on the phosphate ion is indeed -3. This is significant in many chemical contexts, as it indicates how phosphate interacts with other ions and molecules, particularly in biological systems and in the formation of compounds such as phosphates in fertilizers. Recognizing the charge is essential for understanding the ion's behavior in chemical reactions and its role in biological processes like energy transfer (e.g., ATP).