Based on the solubility rules, which one of the following should be soluble in water?

(NH4)3PO4 is soluble in water since it contains an ammonium ion (NH4+), and all substances that contain ammonium are soluble in water. In addition, all compounds that contain phosphate groups (PO4-3) are insoluble unless combined with a group one ion (Na+, Li+, K+, etc) or an ammonium ion.