Which of the following is classified as a strong acid?

Hydrochloric acid is considered a strong acid because it completely dissociates in water to yield hydrogen ions (H⁺) and chloride ions (Cl⁻). This full dissociation means that in solution, the concentration of hydrogen ions is equal to the concentration of the acid, resulting in a low pH and a strong acidic environment.

In contrast, acetic acid, carbonic acid, and ascorbic acid are classified as weak acids. These acids do not fully dissociate in water; instead, they establish an equilibrium between the undissociated acid and the ions. For example, acetic acid only partially ionizes in solution, resulting in a lower concentration of hydrogen ions compared to a strong acid. Similarly, carbonic acid and ascorbic acid partially dissociate, leading to a relatively higher pH than hydrochloric acid at the same concentration.

Thus, hydrochloric acid's complete dissociation characterizes it as a strong acid, distinguishing it clearly from the choices provided.