alleryA buffer solution is most resistant to pH change when:
A[Acid] ≫ [Salt]
B[Acid] = [Salt]
C[Salt] ≫ [Acid]
DSalt is absent
Answer & Solution
Correct answer: B. [Acid] = [Salt]
1. Henderson–Hasselbalch: pH = pKa + log([Salt]/[Acid]).
2. Buffer capacity is MAXIMAL when [Salt] = [Acid] — small additions of acid/base change the ratio least.
3. At this point pH = pKa.
_Source: syllabus Chem Ch 7 §7.12 Buffer Solutions_
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