**Core Concept**
The buffering capacity of a buffer solution is a measure of its ability to resist changes in pH when small amounts of acid or base are added. This capacity is maximum at the pH at which the concentration of the conjugate base and the weak acid are equal, as this is the point where the buffer can most effectively neutralize added hydrogen or hydroxide ions.

**Why the Correct Answer is Right**
The buffering capacity of a buffer solution is maximum at its pKa, which is the pH at which the weak acid is 50% dissociated. At this pH, the concentration of the conjugate base and the weak acid are equal, allowing the buffer to most effectively neutralize added hydrogen or hydroxide ions. This is because the equilibrium between the weak acid (HA) and its conjugate base (A-) is at its midpoint, and the buffer can most effectively counteract changes in pH by reacting with added H+ or OH- ions.

**Why Each Wrong Option is Incorrect**
* **Option A:** This is not a valid answer choice, as the question is incomplete.
* **Option B:** This option is incorrect because the buffering capacity of a buffer solution is not maximum at its pH 7, as this is the pH of a neutral solution, not a buffer.
* **Option D:** This option is incorrect because the buffering capacity of a buffer solution is not maximum at its pH 14, as this is the pH of a strongly basic solution, not a buffer.

**Clinical Pearl / High-Yield Fact**
The Henderson-Hasselbalch equation can be used to calculate the pH of a buffer solution: pH = pKa + log10([A-]/[HA]). This equation is essential for understanding how to prepare and use buffer solutions in clinical settings.

**Correct Answer: C. pH equal to pKa.**