Arrange the following in decreasing order of their acidic strength: $C_6H_5COOH$,$FCH_2COOH$,$NO_2CH_2COOH$. Give an explanation for the arrangement.

(A) The decreasing order of acidic strength is: $NO_2CH_2COOH > FCH_2COOH > C_6H_5COOH$.
Explanation: The acidity of carboxylic acids depends on the stability of the carboxylate ion (conjugate base) formed after the loss of a proton. Electron-withdrawing groups $(EWG)$ stabilize the carboxylate ion by dispersing the negative charge through the inductive effect ($-I$ effect). The strength of the $-I$ effect follows the order: $-NO_2 > -F$. The nitro group $(-NO_2)$ is a stronger electron-withdrawing group than the fluorine atom $(-F)$,making $NO_2CH_2COOH$ the most acidic. $C_6H_5COOH$ (benzoic acid) is the least acidic among these because the phenyl group is less electron-withdrawing compared to the inductive effect of $-F$ and $-NO_2$ groups attached to the alpha-carbon.