What does a base do in terms of hydrogen ions and hydroxide ions?

In the context of acid-base chemistry, a base is defined as a substance that can either take up hydrogen ions (H⁺) or release hydroxide ions (OH⁻) into solution. This duality is crucial for understanding the behavior of bases in different chemical environments.

When a base accepts hydrogen ions, it reduces the concentration of free hydrogen ions in a solution, thereby increasing the pH and making the solution more basic (or alkaline). On the other hand, when a base releases hydroxide ions, it directly contributes to an increase in the OH⁻ concentration, which also raises the pH and promotes a more basic environment.

This dual action of bases makes them fundamental in various chemical reactions, particularly in neutralizing acids, where they react with hydrogen ions to form water and a salt.

Overall, option C encompasses the complete definition of a base, highlighting both its ability to take up hydrogen ions and its capacity to release hydroxide ions, thereby influencing the overall acidity or basicity of a solution.