In general chemistry, which statement best defines a buffer and its primary use?

• A. A buffer is a neutral salt solution and is used to set the pH permanently at $7$ regardless of what is added.
• B. A buffer is a solution with a very high concentration of a strong acid and is used to keep pH constant by overwhelming any added base.
• C. A buffer is a solution that rapidly reacts to eliminate all $H_{+}$ ions and is used to make solutions more acidic.
• D. A buffer is a solution that contains a weak acid and its conjugate base (or a weak base and its conjugate acid) and is used to resist changes in pH when small amounts of acid or base are added.

Answer: (D)