* Ammonium (NH₄⁺) is a polyatomic ion with a positive charge.

* Phosphate (PO₄³⁻) is another polyatomic ion with a negative charge.

Ionic compounds are formed when a metal (or a positively charged polyatomic ion) bonds with a nonmetal (or a negatively charged polyatomic ion). In ammonium phosphate, the positive ammonium ion forms an electrostatic attraction with the negative phosphate ion.

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