How the picric acid is vary strong?

Picric acid is a strong acid due to the following factors:

1. Resonance Stabilization of the Anion: Picric acid undergoes resonance, which involves the delocalization of electrons within the molecule. This resonance stabilizes the conjugate base (picrate ion) and makes it a weaker base. The more stable the conjugate base, the stronger the acid.

2. Electron-withdrawing Nitro Groups: Picric acid contains three nitro groups (-NO2) attached to the benzene ring. These nitro groups are strong electron-withdrawing groups, which means they pull electrons away from the oxygen atoms in the carboxylic acid group. This electron withdrawal weakens the O-H bond, making it easier for the hydrogen ion (H+) to dissociate and donate a proton.

3. Mesomeric Effect: The nitro groups in picric acid also contribute to the mesomeric effect. Mesomerism is a phenomenon where electrons are delocalized between atoms or groups of atoms, resulting in multiple possible structures. In the case of picric acid, the nitro groups can donate electrons to the benzene ring, which further stabilizes the conjugate base and increases the acidity of the compound.

4. Inductive Effect: The electron-withdrawing nature of the nitro groups also has an inductive effect, which involves the transfer of electrons through covalent bonds. The electronegative nitro groups pull electrons away from the carbon atoms in the benzene ring, making them more positive. This positive charge is then transferred to the oxygen atoms in the carboxylic acid group, further weakening the O-H bond and enhancing the acidity of picric acid.

In summary, the resonance stabilization of the conjugate base, the presence of electron-withdrawing nitro groups, the mesomeric effect, and the inductive effect all contribute to the strong acidity of picric acid. These factors make picric acid a more acidic compound compared to other carboxylic acids.