Arrange the following in the increasing order of their acidic strength \table {\FCH}_2 {\COOH},, {\F}_3 {\C} {\COOH},, {\CCl}_3 {\COOH},, {\O}_2 {\NCH}_2 {\COOH}; \I,, \II,, \III,, \IV;

Correct Answer is : I < IV < III < II