Among the given compounds, the most susceptible to nucleophilic attack at the carbonyl group is:
As we learnt in
Those e- rich chemical species having capacity to attack e-deficient portion of substrate.
Nucleophile must have complete octet and atleast one lone pair
Lesser the electron density of acyl carbon atom, more is the susceptibility of a nucleophile attack.
The Cl atom has strong -I effect and weakest + R effect. Because of the weak bond between the small size C-atom and the large size Cl atom . Thus in CH3COCl, acyl carbon has least electron denisty and hence more susceptible for nucleophilic attack.