Which one of the following is the correct molecular formula of ammonium carbonate if the valency of ammonium ion is (+1) and carbonate anion is (-2) ?

The chemical formula of a compound is determined by the valency of its constituent ions, ensuring electrical neutrality. The ammonium ion is a polyatomic cation with a formula of NH4+ and a valency of +1. The carbonate ion is a polyatomic anion with a formula of CO3^2- and a valency of -2. To balance the charges, two ammonium ions (total charge +2) are required for every one carbonate ion (total charge -2). This results in the molecular formula (NH4)2CO3 [1]. The use of parentheses around the ammonium ion indicates that the entire polyatomic group is doubled to satisfy the valency requirements. This compound is an ammonium salt of carbonic acid and contains both ionic bonds between the cations and anions and covalent bonds within the polyatomic ions themselves [1].

Sources

1. [1] https://en.wikipedia.org/wiki/Ammonium_carbonate