Which characteristic distinguishes a strong acid from a weak acid?

The distinguishing characteristic of strong acids is that they completely ionize in solution, which means that they dissociate entirely into their respective ions when dissolved in water. This process results in a high concentration of hydrogen ions (H⁺) in the solution, leading to a lower pH and greater acidity. This complete ionization is what allows strong acids to exhibit their characteristic properties, such as their ability to conduct electricity and their vigorous reactivity with bases and metals.

In contrast, weak acids only partially ionize in solution, producing a lower concentration of hydrogen ions. This results in a higher pH compared to strong acids and generally indicates a less aggressive acidity.

The other options do not accurately reflect the fundamental distinction between strong and weak acids. For instance, the assertion that weak acids produce more gas is not universally true and depends on specific reactions rather than the intrinsic strength of the acid itself. The claim that strong acids are always organic is incorrect, as many strong acids (like hydrochloric acid and sulfuric acid) are inorganic. Lastly, the boiling points of weak acids versus strong acids cannot be generalized, as boiling points are influenced by various factors, including molecular structure and intermolecular forces, rather than the strength of the acid.