Answer is: B because it has a lower activation energy.
For all chemical reaction some energy is required and that energy is called activation energy (energy that needs to be absorbed for a chemical reaction to start), activation energy for reaction B is lower that for reaction A.
Catalysis is the increase in the rate of a chemical reaction due to the participation of an additional substance called a catalyst.
Chemical reactions occur faster with a catalyst because they require less activation energy.
The solution shall contain only (and water) at the equivalence point. Both potassium hydroxide and nitric acid exist as strong electrolytes. As a result, , the salt derived from a reaction between the two species would undergo hydrolysis of a negligible extent. This neutralization reaction therefore be neutral at the equilibrium point.
The question states that the solution is "titrated with a ... nitric acid solution" indicating that is added to the initially-basic solution. PH value of the solution would keep decreasing as the volume of the acid added increases. The final solution would be acidic as it contains not only water and , but some as well. Bromothymol blue would therefore demonstrates a yellow color, the color it present in an acidic solution, at the end of the titration.