Above reaction is known as:

The correct answer is Option (3) → Rosenmund Reaction

In the Rosenmund reduction an acyl chloride is hydrogenated over palladium on barium sulphate. The barium sulphate (often with a little sulphur or quinoline) partly poisons the palladium, so the reduction stops at the aldehyde instead of going on to the alcohol. Here an acyl chloride gives an aldehyde:

    \( \displaystyle \ce{RCOCl + H2} \xrightarrow{\ce{Pd-BaSO4}} \ce{RCHO + HCl} \)

So the reaction is the Rosenmund reaction.

Why the other options are incorrect

• Option (1) Etard Reaction — Incorrect. It oxidises the methyl group of toluene to an aldehyde with chromyl chloride in \( \ce{CS2} \): a chromium complex forms first and is hydrolysed to benzaldehyde. It starts from a methylarene, not an acyl chloride:

      \( \displaystyle \ce{C6H5CH3} \xrightarrow[\text{(ii) }\ce{H3O+}]{\text{(i) }\ce{CrO2Cl2},\ \ce{CS2}} \ce{C6H5CHO} \)

• Option (2) Stephen Reaction — Incorrect. It reduces a nitrile with stannous chloride and hydrochloric acid to an imine, which is hydrolysed to the aldehyde. It starts from a nitrile, not an acyl chloride:

      \( \displaystyle \ce{RCN + SnCl2 + HCl -> RCH=NH} \xrightarrow{\ce{H3O+}} \ce{RCHO} \)

• Option (4) Swarts Reaction — Incorrect. It makes an alkyl fluoride by heating an alkyl chloride or bromide with a metallic fluoride such as AgF, \( \ce{Hg2F2} \), \( \ce{CoF2} \) or \( \ce{SbF3} \); no aldehyde is formed:

      \( \displaystyle \ce{H3C-Br + AgF -> H3C-F + AgBr} \)

NCERT (2026-27 edition):
From Acyl Chloride (Acid Chloride)

Note: The same/similar question has been asked in different years by NTA as per the details given below: