The correct choice is (a) Hydrolysis of an ester to a carboxylic acid using water
Explanation: Pseudo first order reactions are the ones in which the concentration of one of the reactants is used in excess to convert higher order reactions to 1st order. As water is used as solvent in esterification reaction, its concentration is in huge excess compared to the ester. Thus, the reaction is pseudo first order for the ester.