Which of the following solutions has a higher concentration of hydroxide ions?

A basic solution is characterized by a higher concentration of hydroxide ions (OH⁻) compared to acidic and neutral solutions. In such solutions, the pH level is above 7, which indicates that there is an excess of hydroxide ions present. These ions can result from the dissociation of bases in water, which leads to an increase in the concentration of hydroxide ions.

In contrast, an acidic solution contains a higher concentration of hydrogen ions (H⁺), resulting in a lower pH (below 7) and consequently fewer hydroxide ions. A neutral solution, with a pH of 7, has equal concentrations of hydrogen and hydroxide ions, while an aqueous solution simply refers to a solution where water is the solvent and does not necessarily indicate a particular concentration of hydroxide ions.

Thus, the fundamental property of basic solutions, with their surplus of hydroxide ions, makes it clear why this choice is the correct answer regarding higher hydroxide ion concentration.