Which of the following is the correct chemical formula for calcium phosphate?

• A. Ca3(PO4)2
• B. CaPO4
• C. Ca2P2O7
• D. Ca3P2O7

Answer: (A)

Calcium phosphate is an ionic compound made from Ca2+ ions and the phosphate unit PO4^3-. To be neutral, the total positive charge must balance the total negative charge. Three Ca2+ ions give +6, and two PO4^3- units give 2 × (-3) = -6, so Ca3(PO4)2 is neutral and matches the expected stoichiometry for this salt. The other options either don’t balance to neutrality in the same way or represent different phosphate species: CaPO4 would leave an overall mismatch in charge, Ca2P2O7 is calcium pyrophosphate (a different compound with a distinct formula), and Ca3P2O7 would not balance charges properly. So Ca3(PO4)2 is the correct formula for calcium phosphate.