Which of the following is considered a strong acid?

The chosen answer identifies HBr, or hydrobromic acid, as a strong acid. Strong acids are characterized by their complete dissociation in water, meaning they release all of their hydrogen ions into the solution, resulting in a high concentration of H⁺ ions.

HBr is classified as a strong acid because it dissociates completely in aqueous solution, making it very effective at donating protons (H⁺) and contributing to the acidity of the solution. In contrast, other acids listed do not dissociate completely. For example, HClO2, known as chlorous acid, and H2SO3, or sulfurous acid, only partially dissociate in water, which is why they are considered weak acids rather than strong ones. HF, or hydrofluoric acid, while it is a noteworthy acid, is also a weak acid due to its ability to partially ionize in solution, forming a relatively low concentration of H⁺ ions compared to strong acids.

Thus, HBr's complete dissociation sets it apart as a strong acid among the options provided.