Concept:Buffer capacity refers to the amount of acid or base a buffer can absorb before a significant change in pH occurs. It is maximized when the ratio of salt to acid is 1:1.
Formula:$$ \text{pH} = \text{pK}_a + \log \left( \frac{[\text{Salt}]}{[\text{Acid}]} \right) $$
Solution:- When the concentration of the weak acid and its conjugate base are perfectly equal, the ratio is 1, and \( \log(1) = 0 \).
- At this exact point (\( \text{pH} = \text{pK}_a \)), the buffer has an equal ability to neutralize added \( \text{H}^+ \) or \( \text{OH}^- \).
- Therefore, it operates at its maximum theoretical buffer capacity relative to its components.
- Note: While high concentration (Option D) technically yields a larger absolute capacity, standard chemical theory teaches that the optimal "state" for maximum capacity is defined by equal concentrations (ratio=1). This is why B is often the accepted key in these specific exams.
Why other options are incorrect:Low concentration lowers absolute capacity. Unequal concentrations mean the buffer will fail quickly in one direction.
Quality & Fidelity Assurance:
Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.