What kind of smell is ammonia recognized by? 

Pungent

The correct answer is option 4. Pungent.

Ammonia (NH₃) has a pungent and characteristic smell that is easily recognizable. The pungent odor is particularly noticeable at higher concentrations. The smell is due to the release of ammonia gas molecules, and it is often described as sharp, irritating, or similar to that of household cleaning products containing ammonia.

The pungent smell of ammonia is one of its distinctive properties and serves as a warning sign of its presence. In household applications, ammonia is commonly used in cleaning products and may be diluted, but it is still advisable to use it in well-ventilated areas due to its strong odor and potential irritation.