Which of the following is the correct chemical formula for the ionic compound formed between Ca^{2+} and PO_4^{3-} ions?

• A. Ca_2(PO_4)_3
• B. Ca_3(PO_4)_2
• C. CaPO_4
• D. Ca(PO_4)_2

Answer: (B)

Verified step by step guidance

1. Identify the charges of the ions involved: calcium ion is Ca^{2+} and phosphate ion is PO_4^{3-}.
2. Determine the ratio of ions needed to balance the total positive and negative charges so that the compound is electrically neutral.
3. Set up the equation for charge balance: (number of Ca^{2+} ions) \times (+2) + (number of PO_4^{3-} ions) \times (-3) = 0.
4. Find the smallest whole number ratio of Ca^{2+} to PO_4^{3-} ions that satisfies the charge balance equation.
5. Write the chemical formula using the ratio found, placing the number of each ion as subscripts outside the parentheses for polyatomic ions, resulting in the formula Ca_3(PO_4)_2.