Which of the following compounds will give Fehling's solution test?
(A) \( CH_3CHO \)
(B) \( C_6H_5CHO \)
(C) \( CH_3CH_2CHO \)
(D) \( HCHO \)
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A), (C) and (D) only
On heating with an aldehyde, the \( \ce{Cu^2+} \) of Fehling’s reagent is reduced to a reddish brown precipitate of \( \ce{Cu2O} \), and the aldehyde is oxidised to the carboxylate ion:
\( \displaystyle \ce{RCHO + 2Cu^2+ + 5OH- -> RCOO- + Cu2O v + 3H2O} \)
Aliphatic aldehydes give this test; aromatic aldehydes do not.
(A) \(CH_3CHO\) — Correct. Ethanal is an aliphatic aldehyde and gives the red-brown precipitate.
(B) \(C_6H_5CHO\) — Incorrect. Benzaldehyde is an aromatic aldehyde; it does not respond to Fehling's test, although it does give the Tollens’ test of Q47 (ammoniacal silver nitrate).
(C) \(CH_3CH_2CHO\) — Correct. Propanal is an aliphatic aldehyde.
(D) \(HCHO\) — Correct. Methanal is an aliphatic aldehyde and gives the test (with HCHO the copper may even be reduced to the metal).
NCERT (2026-27 edition):
Fehling’s Test
