What do acids produce when dissolved in water?

When acids dissolve in water, they produce positive hydrogen ions. This process occurs because an acid is defined as a substance that donates protons (H⁺ ions) when in an aqueous solution.

A strong acid, for example, completely dissociates into its hydrogen ions and its corresponding anions in water. This generation of hydrogen ions is what characterizes the acidic properties of the solution, leading to a decrease in pH. The presence of free hydrogen ions is also what gives acids their ability to react with bases and participate in various chemical reactions.

The other choices do not align with the behavior of acids in water. Negative hydroxide ions are produced by bases, not acids. Neutral ions do not specifically represent acids or their behaviors. Positive sodium ions can be produced in solutions with sodium-containing acids, but they are not intrinsic to all acids and do not define the acidic nature of a solution like the presence of hydrogen ions does. Thus, the production of positive hydrogen ions is the defining characteristic of acids in aqueous solutions.