Question

Strongest acid among the following is:

• A.
• B.
• C.
• D.

Hint:

The strength of an acid depends on how stable its conjugate base is, because the stronger the acid, the weaker its conjugate base, and the stability of that conjugate base is determined by the electron donating or withdrawing properties of nearby substituents.

Answer 1

The Correct Option is D

Meta-nitrobenzoic acid (option 4) is the strongest acid among the provided options. A nitro group acts as a potent electron-withdrawing substituent, significantly increasing acidity. When located at the meta position, this group stabilizes the conjugate base's negative charge via an inductive effect, enhancing stability relative to other options. The acidity decreases in the following order:
• Trichloroacetic acid: stronger than phenolic hydroxyl groups (options 1 and 3).
• Formic acid: Its strength stems from the absence of electron-donating groups.
• Acetic acid: Weaker due to the electron-donating effect of its methyl group.
• Benzoic acid: The weakest, primarily due to resonance stabilization of the benzene ring.
This illustrates the influence of molecular structure on acidity.