Here's why:

* Strong acids completely ionize in solution, meaning they donate all their hydrogen ions (H⁺) to the solution. Examples include hydrochloric acid (HCl) and sulfuric acid (H₂SO₄).

* Weak acids only partially ionize in solution, meaning they only donate some of their hydrogen ions.

Hydrosulfuric acid is a weak acid because it only partially ionizes in solution. It is also known as hydrogen sulfide gas and is a colorless, flammable gas with a pungent odor resembling rotten eggs.