2,4,6-Trinitrophenol is
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Strong Acid
Phenols are acidic because the phenoxide ion is stabilised by resonance. An electron-withdrawing –NO2 group at an ortho or para position spreads the negative charge further and increases the acidity. 2,4,6-Trinitrophenol (picric acid) has three –NO2 groups, at both ortho positions and the para position, so the O–H proton is released very easily:
\( \displaystyle \ce{(O2N)3C6H2OH + H2O <=> (O2N)3C6H2O^- + H3O+} \)
Its pKa (about 0.4) is far below that of phenol (10.0) and even below that of carboxylic acids, so picric acid is a strong acid.
Why the other options are incorrect
Option (2) Strong Base — Incorrect. Picric acid has no basic group; the lone pairs on the phenolic O are delocalised into the ring.
Option (3) Weak Base — Incorrect. Phenols do not accept protons in water; the nitro groups make the ring even poorer in electrons.
Option (4) Amphoteric — Incorrect. An amphoteric substance must also act as a base; picric acid shows only acidic behaviour.
NCERT (2026-27 edition):
Nitration – “… 2, 4, 6 - Trinitrophenol is a strong acid due to the presence of three electron withdrawing –NO2 groups which facilitate the release of hydrogen ion.”