Final answer:
The IUPAC name of (NH4)3PO4 is ammonium phosphate.
Step-by-step explanation:
The IUPAC name of the compound whose formula is (NH4)3PO4 is ammonium phosphate. In this compound, the NH4 part represents the ammonium ion, and PO4 represents the phosphate ion. To determine the IUPAC name, we combine the name of the cation (ammonium) with the name of the anion (phosphate), since both ions have charges that balance each other out in the compound's neutral form. The correct answer to the student's question is therefore option A) Ammonium phosphate.