Which of the following reagent is not used to convert aldehyde into alcohol?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \(Sn/HCl\)
An aldehyde is reduced to a primary alcohol when hydrogen adds across the C=O bond. Metal hydrides and catalytic hydrogenation do this; tin and hydrochloric acid do not.
Option (1) \(H_2/Pd\) — Used to convert an aldehyde into an alcohol. Hydrogen on a palladium (or nickel, platinum) catalyst adds across C=O:
\( \displaystyle \ce{CH3CHO + H2} \xrightarrow{\ce{Pd}} \ce{CH3CH2OH} \)
Option (2) \(LiAlH_4\) — Used to convert an aldehyde into an alcohol. Lithium aluminium hydride delivers a hydride ion to the carbonyl carbon; work-up with acid gives the primary alcohol:
\( \displaystyle \ce{CH3CHO} \xrightarrow[\text{(ii) }\ce{H3O+}]{\text{(i) }\ce{LiAlH4}} \ce{CH3CH2OH} \)
Option (3) \(NaBH_4\) — Used to convert an aldehyde into an alcohol. Sodium borohydride is a milder hydride reagent that reduces aldehydes and ketones:
\( \displaystyle \ce{CH3CHO} \xrightarrow[\text{(ii) }\ce{H3O+}]{\text{(i) }\ce{NaBH4}} \ce{CH3CH2OH} \)
Option (4) \(Sn/HCl\) — Not used to convert an aldehyde into an alcohol. Tin and hydrochloric acid are used to reduce nitro compounds to amines, for example nitrobenzene to aniline:
\( \displaystyle \ce{C6H5NO2 + 6[H]} \xrightarrow{\ce{Sn/HCl}} \ce{C6H5NH2 + 2H2O} \)
NCERT (2026-27 edition):
Reduction
