What differentiates a strong acid from a weak acid?

The distinction between a strong acid and a weak acid is primarily based on their dissociation in water. A strong acid fully dissociates into its ions when dissolved, resulting in a high concentration of hydrogen ions (H⁺) in solution. This complete dissociation means that all of the acid molecules break apart into their constituent ions, leading to a low pH value, typically below 3.

In contrast, a weak acid only partially dissociates in solution, which means that only a fraction of the acid molecules release hydrogen ions. This results in a lower concentration of hydrogen ions compared to a strong acid, contributing to a higher pH value.

Thus, the correct choice identifies that while strong acids dissociate completely, weak acids only dissociate partially, making this distinction crucial for understanding acid strength and behavior in chemical reactions.