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 given options a nitro group is a strong electron-withdrawing substituent which increases the acidity. When substituted at the meta position, the nitro group stabilizes the negative charge of the conjugate base through inductive effect, making it more stable compared to the options. The decreasing order of acidity is:
• Trichloroacetic acid: phenolic hydroxyl groups (option 1 and 3) weaker
• Formic acid: Strong due to the absence of electron-donating groups.
• Acetic acid: Weaker as the methyl group has an electron-donating effect.
• Benzoic acid: Weakest due to resonance stabilization of the benzene ring.
This shows the relationship between molecular structure and acidity.