Which of the following is the correct chemical formula for the ionic compound formed between NH_4^+ and PO_4^{3-}?

• A. NH_4(PO_4)_3
• B. NH_4PO_4
• C. NH_4_3PO_4
• D. (NH_4)_3PO_4

Answer: (B)

Verified step by step guidance

1. Identify the charges of the ions involved: ammonium ion is \(\mathrm{NH_4^+}\) with a charge of +1, and phosphate ion is \(\mathrm{PO_4^{3-}}\) with a charge of -3.
2. Determine the ratio of ammonium ions to phosphate ions needed to balance the overall charge to zero. Since phosphate has a charge of -3, you need three ammonium ions (each +1) to balance one phosphate ion.
3. Write the formula by placing the ammonium ion in parentheses with a subscript of 3 to indicate three ammonium ions, followed by the phosphate ion without a subscript (since there is only one). This gives \((\mathrm{NH_4})_3\mathrm{PO_4}\).
4. Check that the total positive charge from ammonium ions (+3) balances the total negative charge from phosphate ion (-3), confirming the compound is electrically neutral.
5. Conclude that the correct chemical formula for the ionic compound formed between \(\mathrm{NH_4^+}\) and \(\mathrm{PO_4^{3-}}\) is \((\mathrm{NH_4})_3\mathrm{PO_4}\).