Which of the following acids is a strong acid used in the laboratory?

The chosen answer is correct because sulfuric acid (H2SO4) is classified as a strong acid. Strong acids are defined by their ability to completely dissociate into their ions in an aqueous solution, which means they release protons (H+) efficiently. Sulfuric acid not only fulfills this criterion but is also commonly used in laboratories for various applications such as dehydrating agents, titrations, and as a catalyst in chemical reactions.

In contrast, acetic acid (CH3COOH) is a weak acid that only partially dissociates in solution, making it less effective for laboratory reactions that require a strong acidic environment. Hydrofluoric acid (HF) is also classified as a weak acid, despite being highly corrosive; it does not completely ionize in water. Ammonium ion (NH4+) is not an acid in its own right but rather the conjugate acid of ammonia; it can donate protons, but it is not considered a strong acid either.

Therefore, in the context of laboratory use and dissociation characteristics, sulfuric acid is decidedly the strong acid among the provided options.