What distinguishes a strong acid from a weak acid?

A strong acid is characterized by its ability to completely dissociate in water, which means that when it is dissolved, it breaks apart into its ions fully, releasing all of its available hydrogen ions. This results in a high concentration of hydrogen ions (H⁺) in the solution, leading to a lower pH and a stronger acidic behavior.

In contrast, a weak acid only partially dissociates in solution. This means that not all of the acid molecules release their hydrogen ions; as a result, the concentration of hydrogen ions is lower than that in a strong acid solution, reflecting its weaker acidic nature. The degree of dissociation is a key factor that distinguishes strong acids from weak acids, hence making the ability to fully dissociate the defining property of strong acids.

The other choices do not accurately describe the behavior of acids in terms of their dissociation and consequent acidity levels.