Ammonium carbonate is not an insoluble salt. In fact, it is soluble in water.

Here's why:

* Ammonium salts are generally soluble. Ammonium (NH₄⁺) is a positively charged ion that forms ionic bonds with negatively charged anions. These bonds are usually weak enough to allow the salt to dissolve in water.

* Carbonate salts are typically insoluble, with exceptions. While most carbonates are insoluble, ammonium carbonate is an exception to this rule. This is due to the strong tendency of ammonium ions to form soluble compounds.

Therefore, ammonium carbonate readily dissolves in water, making it a soluble salt.