Answer
A. estimate the pH of a buffer solution.
Step-by-step explanation
The Henderson–Hasselbalch equation can be used to calculate the amount of acid and conjugate base to be combined for the preparation of a buffer solution having a particular pH, as shown below.
Therefore, the Henderson–Hasselbalch equation can be used to estimate the pH of a buffer solution by approximating the actual concentration ratio as the ratio of the analytical concentrations of the acid and of salt.
The correct answer is: option A. estimate the pH of a buffer solution.