To increase the pH of a solution of acid, you would want to decrease the concentration of hydrogen ions (\[H^+\]) in the solution.
A. Increasing the dissociation constant (Kₐ) would typically mean that the acid is stronger and will dissociate more, releasing more hydrogen ions into the solution, which would actually decrease the pH (make it more acidic). Therefore, this option would not help in increasing the pH.
B. Decreasing the strength of the acid means that the acid is less capable of donating protons (or hydrogen ions) to the solution. A weaker acid will dissociate less, resulting in fewer hydrogen ions in the solution and, as a result, a higher pH.
Thus, the correct choice that would increase the pH of a solution of acid is B. decreasing the strength of the acid.