It's ammonia (NH3) that has the characteristic pungent, strong odor.

Here's why:

* Ammonium salts are ionic compounds: They consist of an ammonium cation (NH4+) and an anion like chloride (Cl-) in ammonium chloride (NH4Cl).

* Ammonia is a gas: It readily escapes from solutions of ammonium salts, especially when the solution is heated or made basic.

* The smell is due to ammonia: The pungent smell we associate with ammonium salts is actually the smell of ammonia gas that is released from the salt.

In summary, the pungent smell is not directly from the ammonium salt itself, but from ammonia gas that is released when the salt decomposes.