The compounds which give positive Fehling's test are :
Choose the correct answer from the options given below :

Solution

Chemistry ma’am · 3 steps

Fehling's test needs an aliphatic CHO or an α-hydroxy ketone; a CHO sitting on the ring does not count.

1. What Fehling's needs. Fehling's solution is a mild oxidant that turns blue Cu²⁺ into a red precipitate of Cu₂O. Aliphatic aldehydes reduce it, but aromatic aldehydes, where -CHO is attached directly to the benzene ring, do not.
2. Ketone exception. Ordinary ketones give a negative test. An α-hydroxy ketone (-CO-CH₂OH), like fructose, gives a positive one, because in the alkaline medium it rearranges (through an enediol) into an aldehyde.

   Compound	Group	Fehling's test
   (A) Benzaldehyde	-CHO directly on the ring (aromatic aldehyde)	Negative
   (B) Acetophenone	Ordinary ketone	Negative
   (C) Fructose	α-hydroxy ketone, HOCH₂-CO⁻	Positive
   (D) Acetaldehyde	Aliphatic aldehyde	Positive
   (E) Phenylacetaldehyde	-CHO on a CH₂, not on the ring	Positive

3. So. (C), (D) and (E) give a positive Fehling's test, which is option (d).

The idea to keep. For Fehling's test, check where the CHO is attached: on a ring carbon, negative; on an alkyl carbon, even next to a phenyl, positive. Also remember that α-hydroxy ketones like fructose give a positive test.

Answer from the NTA final answer key. Solution by PrepWiser.