pKa is highest for

R-COOH+H2O⇌R-COO-+H3O+ ; greater the stability of R-COO- more will be the acidic strength in aqueous solution (ka) . +I groups intensify the negative charge of carboxylate ion (RCOO-) and destabilize it. Thus EDG decreases the acidic strength of carboxylic acids.ka of 1 > 2 > 3 > 4pka of 1 < 2 < 3 < 4.