Which property is NOT characteristic of strong acids?

Strong acids are defined by their ability to completely dissociate in aqueous solution, which means they release all of their hydrogen ions (or protons) into the solution, forming hydronium ions. This complete dissociation is a fundamental characteristic that distinguishes strong acids from weak acids, which only partially dissociate.

The first characteristic, exhibiting a sour taste, is typical of acidic solutions in general, although safety precautions should always be taken when tasting any chemical. High conductivity in solution is also a hallmark of strong acids since the complete ionization leads to a significant concentration of ions, enhancing the solution's ability to conduct electricity. Lastly, the production of hydronium ions is a direct result of the dissociation of strong acids in water, underscoring their strength.

In contrast, the statement that strong acids do not dissociate completely contradicts the definition of strong acids. Therefore, this characteristic does not apply and is the correct answer to the question.