In which type of solution do hydrogen ions become less concentrated, leading to a pH greater than 7?

The correct answer is found in the nature of a base. A base is defined as a substance that reduces the concentration of hydrogen ions (H+) in solution, which results in an increase in pH, making it greater than 7. This is because bases can either accept hydrogen ions or release hydroxide ions (OH-) into the solution. When hydroxide ions are present, they react with hydrogen ions to form water, thus lowering the overall concentration of H+ ions.

A pH greater than 7 indicates an alkaline environment, characteristic of basic solutions, where the balance shifts away from hydrogen ions towards hydroxide ions.

In contrast, an acid would increase hydrogen ion concentration, leading to a pH less than 7, while a neutral solution, like pure water, maintains a balance that results in a pH of exactly 7. An aqueous solution refers broadly to any solution where water is the solvent and could be acidic, neutral, or basic, but it does not specifically denote the decrease in hydrogen ion concentration necessary for a basic solution.