Among the following compounds, the increasing order of their acidic strength is
(A) m-Nitrophenol
(B) m-Cresol
(C) Phenol
(D) p-Nitrophenol
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (B), (C), (A), (D)
The acidity of a phenol depends on how well its phenoxide ion is stabilised. Two effects decide it:
Electron withdrawing –NO2 group: increases acidity. At the para (or ortho) position it acts by both −R and −I effects, since the negative charge can move onto the nitro group. At the meta position only the weaker −I effect works. So p-nitro > m-nitro in acidity.
Electron donating –CH3 group: by its +I effect it pushes electrons into the ring, destabilises the phenoxide ion and makes the phenol less acidic than phenol.
Matching the given compounds:
(B) m-Cresol: electron donating \( \ce{CH3} \).
(C) Phenol: no substituent.
(A) m-Nitrophenol: −I effect only.
(D) p-Nitrophenol: −R and −I effects.
Shortcut: Options (1) and (3) both start with m-cresol (B) and end with p-nitrophenol (D). Phenol is weaker than any nitrophenol, so (C) must come before (A), which leaves only Option (3).
NCERT (2026-27 edition):
Acidity of Phenols – …
Note: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| 07-06 S2 | – | 29-05 S1 | – | – |