What is the characteristic feature of a strong acid?

A strong acid is defined by its ability to completely dissociate in an aqueous solution. This means that when a strong acid is added to water, it breaks down entirely into its ions, producing a high concentration of hydrogen ions (H⁺) in the solution. This complete ionization is what leads to the characteristic properties of strong acids, including their ability to conduct electricity, their potent reactivity with bases and metals, and their low pH values.

The complete dissociation also means that the concentration of hydrogen ions directly reflects the concentration of the acid itself, which is why strong acids have a significantly lower pH compared to weak acids, which only partially ionize. This characteristic sets strong acids apart in terms of reactivity and strength when compared to weaker acids, which do not fully dissociate in solution. Thus, the defining feature of a strong acid is its complete dissociation in solution.