A buffer is a solution that resists changes in pH when small amounts of an acid or base are added. Therefore, the statement that best describes a buffer is:
a. A buffer prevents the pH of a solution from changing when an acid or base is added.
Buffers are important in many biological and chemical processes because they help maintain a stable pH environment. When acids or bases are introduced, buffers can absorb excess hydrogen ions (H+) or hydroxide ions (OH-), thereby minimizing any significant shift in pH.