What is the formula of ammonium carbonate?

The formula for ammonium carbonate is \((NH_4)_2CO_3\).

### Explanation:

1. **Understanding Ammonium and Carbonate:**
- **Ammonium Ion (\(NH_4^+\))**: This is a positively charged polyatomic ion. Each ammonium ion consists of one nitrogen atom (N) and four hydrogen atoms (H).
- **Carbonate Ion (\(CO_3^{2-}\))**: This is a negatively charged polyatomic ion. It consists of one carbon atom (C) and three oxygen atoms (O) and carries a charge of -2.

2. **Combining the Ions:**
- To form ammonium carbonate, we need to balance the charges of the ammonium and carbonate ions. Since each ammonium ion has a charge of +1, two ammonium ions will have a total charge of +2 (\(2 \times +1\)).
- The carbonate ion has a charge of -2. To balance the positive and negative charges, we combine two ammonium ions with one carbonate ion.

3. **Writing the Formula:**
- The resulting formula shows that there are two ammonium ions for every carbonate ion, resulting in \((NH_4)_2CO_3\).

### Summary:
Thus, the complete chemical formula for ammonium carbonate is \((NH_4)_2CO_3\).