Which of the following is an example of a strong acid?

Hydrochloric acid (HCl) is classified as a strong acid because it completely dissociates in aqueous solution. This means that when HCl is dissolved in water, it separates entirely into hydrogen ions (H⁺) and chloride ions (Cl⁻). The full dissociation leads to a high concentration of H⁺ ions in the solution, resulting in a significant decrease in pH, which is characteristic of strong acids.

In contrast, acetic acid only partially dissociates in solution, meaning that not all of the acetic acid molecules release H⁺ ions. Similarly, citric acid is a weak acid that also does not fully dissociate in solution. Sodium bicarbonate is a weak base that can react with acids but does not act as a strong acid itself.

The complete dissociation of strong acids like HCl is a crucial property that defines their strength, distinguishing them from weak acids that do not fully ionize.