Which of the following is a weak acid?

The choice of H2CO3, which is carbonic acid, as a weak acid is accurate because it partially ionizes in aqueous solution. Unlike strong acids such as H2SO4 (sulfuric acid) and HNO3 (nitric acid), which completely dissociate to release protons (H+ ions), carbonic acid only partially dissociates.

In water, H2CO3 can dissociate into H+ and HCO3− (bicarbonate ions). The fact that it does not release all of its hydrogen ions makes it a weak acid. This behavior is characteristic of weak acids, which reach an equilibrium state rather than undergoing complete ionization.

In contrast, NaOH (sodium hydroxide) is a strong base, not an acid, and therefore cannot be considered in the context of weak acids. Understanding the distinction between weak and strong acids is crucial for anyone studying aqueous chemistry, as it affects pH, conductivity, and the behavior of acid-base reactions in solution.