Solved: CHEMISTRY Question for NEET

NEET CHEMISTRYMedium

The most suitable reagent for the following conversion is-

$Hg^{2+}/H^+, H_2O$

$Na/\text{liquid } NH_3$

$H_2, Pd/C, \text{quinoline}$

$Zn/HCl$

Identify the Reagent: The reagent specified in Option 3 is dihydrogen gas ( $H_2$ ) in the presence of palladium supported on charcoal ( $Pd/C$ ) and deactivated with quinoline or sulphur. This specific combination is known as Lindlar’s catalyst [NCERT 11th, Ch 13, Sec 13.3.4; Source 125].
Function: Lindlar's catalyst is used for the partial reduction of alkynes to cis-alkenes. The reaction involves the syn-addition of hydrogen. $RC\equiv CR' + H_2 \xrightarrow{Pd/C, \text{quinoline}} \text{cis-alkene}$
Context (NEET 2019): In the original exam question, the reaction scheme (missing from the input text) depicted the conversion of but-2-yne to cis-but-2-ene.
Analysis of Other Options:

$Na/\text{liquid } NH_3$ (Birch reduction) reduces alkynes to trans-alkenes . $Hg^{2+}/H^+, H_2O$ is used for the hydration of alkynes to form ketones or aldehydes. $Zn/HCl$ is a reducing agent typically used for alkyl halides or Clemmensen reduction.

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