Here's how to understand this formula:

* Ammonium (NH₄⁺): Ammonium is a polyatomic ion with a +1 charge.

* Sulfite (SO₃²⁻): Sulfite is also a polyatomic ion, but it has a -2 charge.

* Balancing Charges: To form a neutral compound, we need two ammonium ions (2 x +1 = +2) to balance the -2 charge of the sulfite ion. This leads to the formula (NH₄)₂SO₃.