Which of the following compounds will show highest acidic strength?

2,4,6-Trinitrophenol

The correct answer is Option (1) → 2,4,6-Trinitrophenol
2,4,6-Trinitrophenol shows the highest acidic strength.
Acidity of phenols increases when electron-withdrawing groups like nitro groups are attached to the benzene ring, especially at ortho and para positions. Nitro groups stabilize the phenoxide ion by withdrawing electron density through both inductive and resonance effects.

Comparison:

• Phenol → no nitro group → least acidic

• 2-Nitrophenol → one nitro group → more acidic

• 2,4-Dinitrophenol → two nitro groups → even more acidic

• 2,4,6-Trinitrophenol → three nitro groups → maximum stabilization → most acidic

Therefore, more nitro groups mean stronger acid, and 2,4,6-Trinitrophenol (picric acid) has the highest acidic strength.

Order of acidic strength:

2,4,6-Trinitrophenol > 2,4-Dinitrophenol > 2-Nitrophenol > Phenol