Arrange the following in decreasing order of their acidic strength. Give explanation for the arrangement.

C₆H₅COOH, FCH₂COOH, NO₂CH₂COOH

The decreasing order of their acidic strength:

NO₂CH₂COOH > FCH₂COOH > C₆H₅COOH.

EXPLAINATION:

Electron withdrawing groups like -NO₂, increases the acidity of carboxylic acids by stabilizing the conjugate base through resonance effects, whereas, electron-donating groups decrease the acidity of carboxylic acids by destabilizing the conjugate base through resonance.

We know that the negative inductive effect of nitro group is greater than that of the fluorine atom.

Thus, NO₂CH₂COOH is most acidic among the given three compounds.

Hence, the decreasing order in terms of their acidic strength is:

NO₂CH₂COOH > FCH₂COOH > C₆H₅COOH.