The diagram shows a pH curve produced by adding a strong alkali to a weak acid - AQA - A-Level Chemistry - Question 22 - 2017 - Paper 3

A buffer solution is characterized by its ability to maintain a consistent pH when small amounts of acid or base are added. In the context of the pH curve, this typically occurs at the midpoint of the curve, where the weak acid and its conjugate base are present in similar concentrations. Based on the provided diagram, point B is the only location on the curve where the pH stabilizes and suggests that it has a balance of acidic and basic forms, thus representing a buffer solution.