What defines a strong acid?

A strong acid is defined by its ability to dissociate completely in water, meaning that when a strong acid is dissolved, it releases a high concentration of hydrogen ions (H⁺) into the solution. This complete ionization is what distinguishes strong acids from weak acids, which only partially dissociate and therefore do not produce as many hydrogen ions in solution.

This complete dissociation results in lower pH values, typically around 1 or 2 for strong acids, which indicates a high concentration of H⁺ ions. Strong acids, such as hydrochloric acid (HCl) or sulfuric acid (H₂SO₄), achieve this property because their molecules break apart entirely into their constituent ions when in an aqueous solution.

While some options may suggest other characteristics of acids—such as not dissociating in water, having a high pH, or possessing a sour taste—these do not define strength in terms of acid dissociation. The defining feature of strong acids is their complete ionization in solution.