23-M of NO2 will decrease the e- density on COO- in the anion making it less basic and hence making the conjugate acid highly acidic
similarly -M of Cl shows same effect but due to 3p-2p delocalisation the resonance wont be highly effective hence the conjugate acid will be just slightly acidic than benzoic acid
methoxy grp will show +M effect wich will actually increase e- density on the COO- making it more basic and hence the conjugate acid lesser basic
methyl grp shos similar effect but with the help of +I and HC hence less effective than methoxy grp
hence the order
