Among the given compounds, the most susceptible to nucleophilic attack at the carbonyl group is

Step-by-step solution

Key Idea Lesser the electron density of acyl carbon atom, more will be the susceptibility of nucleophile to attack it. The Cl atom has strong -I effect and weakest + R effect because of the weak -bond between the small sized C -atom and large sized Cl atom. Thus, in CH ₃ COCl , acyl carbon has least electron density and hence, more susceptible for nucleophilic attack.