Answer : 3. "FCH2COOH"
Explanation :

Answer: C) FCH2COOH Explanation: FCH2COOH is the strongest acid out of all .Since the electron withdrawing inductive effect (-I effect) of the halogens decreases in the order   F>Cl> Br> I , therefore the acidic strength of the α- halo acids decreases in the same order.   FCH2COOH  >  ClCH2COOH   >   BrCH2COOH   >   ICH2COOH.