I = ClCH2COOH, II = formic acid, III = CHCl2COOH, IV = C6H5COOH.  Correct acidic strength order is

EWG increase the acidic strength of aliphatic carboxylic acids by-I effect.—I effect of —CF3>—NO2>—CN>—F>—Cl>—Br>—I>—PhEDG decrease the acidic strength of aliphatic carboxylic acids by +I effectAlkyl groups shows +I effect;+I effect increase with increase in chain length and bulkiness of alkyl group.∴ Acidic strength of O2N−CH2−COOH>NC−CH2−COOH>F−CH2−COOH>CH3−COOH>R−CH2−COOHInductive effect weakens as the distance increases.Presence of EWG at α-position makes acetic acid (or) propionic more acidic than formic acid.Let an EWG is present at β-position of acetic acid (or) propionic acid. It is less acidic than formic acid. Thus Cl2CHCOOH>ClCH2COOH>HCOOH>C6H5COOH