What type of solution resists changes in pH when acids or bases are added?

The correct answer is buffer. A buffer solution is designed to maintain a relatively stable pH level even when small amounts of acids or bases are introduced. This is due to the buffer's composition, which typically includes a weak acid and its conjugate base or a weak base and its conjugate acid. When an acid is added, the conjugate base in the buffer reacts with the hydrogen ions (H⁺) from the acid, minimizing the increase in acidity; similarly, when a base is added, the weak acid component of the buffer can donate protons (H⁺), mitigating the rise in pH.

Buffers are essential in many biochemical processes and experiments as they help to stabilize the pH environment necessary for optimal enzyme function and other biochemical reactions. In contrast, pure water does not have buffering capacity and can experience significant changes in pH with the addition of acids or bases. Concentration and electrolyte solutions may influence pH but do not specifically indicate a solution's ability to resist pH changes like a buffer does.