Advanced Placement (AP) Chemistry Practice Exam

An Arrhenius base is defined as a substance that, when dissolved in water, increases the concentration of hydroxide ions (OH⁻) in the solution. This increase in hydroxide ions is what characterizes the behavior of an Arrhenius base.

For example, when sodium hydroxide (NaOH) dissolves in water, it dissociates into sodium ions (Na⁺) and hydroxide ions (OH⁻). The production of these hydroxide ions is crucial because they can react with hydrogen ions (H⁺) in the solution, leading to a decrease in acidity and an increase in the solution’s basicity.

Thus, the correct response highlights the key feature of Arrhenius bases and their role in aqueous solutions, which is the generation of hydroxide ions that contribute to the basic nature of the solution.