Which term describes compounds that reduce the concentration of hydrogen ions in a solution?

• A. Bases
• B. Acids
• C. Salts
• D. Solvent

Answer: (A)

Bases are compounds that reduce the concentration of hydrogen ions in a solution, which raises the pH and makes the solution less acidic. In water, bases do this mainly by either accepting hydrogen ions or by releasing hydroxide ions (OH−) that react with the hydrogen ions to form water. For example, sodium hydroxide dissolves to give OH−, which lowers the free H+ in the solution. This behavior matches how bases act to decrease acidity, fitting the idea of reducing hydrogen-ion concentration. Acids increase hydrogen ions, salts can affect pH in various ways, and solvents are the medium but don’t define a substance by lowering H+. So the term that best describes compounds that reduce hydrogen-ion concentration is bases.