Which of the following is an example of a buffer solution?

A buffer solution is one that can maintain a relatively constant pH when small amounts of an acid or base are added. This is often achieved by a weak acid and its conjugate base. The pair in option B, ethanoic acid (a weak acid) and its conjugate base, acetate, effectively neutralizes added acids or bases. When a small amount of strong acid is added to the buffer solution, the conjugate base can react with the excess H⁺ ions, minimizing the impact on pH. Conversely, if a strong base is added, the weak acid can donate H⁺ ions to counteract the increase in pH.

In contrast, the other options do not fulfill the criteria for a buffer. Sodium chloride in water is a neutral salt solution and does not have the ability to resist pH changes. Hydrochloric acid and sodium hydroxide form a strong acid-strong base reaction, leading to a neutral solution without buffering capacity. Potassium nitrate, like sodium chloride, is a neutral salt in solution and does not provide the required weak acid-conjugate base balance to act as a buffer. Therefore, the correct answer highlights the importance of having both a weak acid and its conjugate base to effectively act as a