How can a strong acid be defined?

A strong acid is defined as one that completely dissociates into ions when dissolved in water. This means that all the acid molecules break apart to release hydrogen ions (H⁺) and the corresponding anions. For example, when hydrochloric acid (HCl) is added to water, it completely dissociates into H⁺ and Cl⁻ ions, resulting in a high concentration of hydrogen ions in the solution. This complete dissociation is what gives strong acids their characteristic properties, such as a very low pH and a high conductivity in solution due to the greater availability of ions.

In contrast, options that describe partial dissociation or weak ionization do not accurately characterize strong acids, as they imply that not all acid molecules break down into ions, which is a defining feature of weak acids. Similarly, a low concentration of hydrogen ions contradicts the very nature of a strong acid, which must have a high concentration of dissociated ions in solution.