Final answer:
A buffer at pH 8.5 with a pK of 7.5 can better buffer the addition of acid, as it has a greater capacity for absorbing protons due to the higher concentration of its conjugate base. The option (A) is correct.
Step-by-step explanation:
A solution of a buffer at a pH of 8.5 with a pK = 7.5 would have more capacity to buffer the addition of an acid. According to the Henderson-Hasselbalch equation, a buffer has its maximum capacity when the pH is equal to the pK. Since the given buffer has a pH higher than its pK, it contains more of the conjugate base, indicating that it is better suited to neutralize added acids rather than bases.
Buffer capacity depends on the concentrations of the weak acid and its conjugate base within the buffer solution. A buffer solution with higher concentrations of these components can absorb more added strong acids or bases before a significant change in pH occurs. It's important also to note that buffers are generally most effective within one pH unit of their pK value. Therefore, option (A) is correct.