What common characteristic do acids share in water?

Acids share the characteristic of donating hydrogen ions (H⁺) when dissolved in water. This is a fundamental property that defines acidic behavior. When an acid is in aqueous solution, it releases protons, which can lead to an increased concentration of hydrogen ions in the solution. This increase in hydrogen ions is what gives acids their acidic properties, such as the ability to change the color of pH indicators, and affects how they interact with bases.

In contrast, concepts like accepting hydrogen ions or producing hydroxide ions relate to other chemical behaviors. Accepting hydrogen ions describes the behavior of bases, not acids. Producing hydroxide ions is also characteristic of bases, which tend to raise the hydroxide ion concentration in solution. Finally, the notion of complete dissociation pertains to strong acids, but not all acids dissociate completely in water; many are weak and only partially dissociate. Therefore, the defining characteristic that applies universally to all acids in aqueous solutions is their ability to donate hydrogen ions.