The reagent used to convert But-2-en-1-ol to But-2-enal is
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → pyridinium Chlorochromate
Oxidising a primary alcohol to an aldehyde needs a mild, selective reagent, because strong oxidising agents carry the oxidation on to the carboxylic acid. Pyridinium chlorochromate (PCC), a complex of chromium trioxide with pyridine and HCl, stops at the aldehyde and does not attack a C=C bond.
But-2-en-1-ol is a primary alcohol that also has a C=C bond, which must stay unchanged in but-2-enal:
So the reagent is pyridinium chlorochromate.
Why the other options are incorrect
Option (1) KMnO4 — Incorrect. It is a strong oxidising agent. It oxidises a primary alcohol all the way to the carboxylic acid and also attacks the C=C bond.
Option (3) Cu/573K — Incorrect. Heated copper at 573 K dehydrogenates a primary alcohol to an aldehyde in the vapour phase; it is not the laboratory reagent for this conversion, PCC is, as it gives the aldehyde in good yield.
Option (4) NaBH4 — Incorrect. It is a reducing agent. It converts aldehydes back into alcohols, the reverse of the required change.
NCERT (2026-27 edition):
Oxidation – …
