The compound formed between ammonium ion (NH₄⁺) and carbonate ion (CO₃²⁻) is ammonium carbonate.

Here's how to determine the formula:

* Ammonium ion: NH₄⁺

* Carbonate ion: CO₃²⁻

To balance the charges, we need two ammonium ions (2+ charge) to neutralize the 2- charge of the carbonate ion.

Therefore, the formula for ammonium carbonate is (NH₄)₂CO₃.