Which of the following is used to convert C=O group to CH2 ? a) Ni/H2/ b) LiAlH4/ c) Zn Hg/HCl/ d) Pd/H2/

The conversion of a carbonyl group ($>\mathrm{C}=\mathrm{O}$) to a methylene group ($-\mathrm{CH}{}_2-$) is achieved through the Clemmensen reduction. This reaction involves the use of zinc amalgam (Zn-Hg) in the presence of hydrochloric acid (HCl) and heat ($\Delta$).

The correct option is: c) $\mathrm{Zn}-\mathrm{Hg}/\mathrm{HCl}/\mathrm{\Delta }$

This reaction reduces the carbonyl group to a methylene group by replacing the oxygen with two hydrogen atoms, forming an alkane. The other options are incorrect because:

• $\mathrm{Ni}/\mathrm{H}{}_2/\mathrm{\Delta }$ is used for hydrogenation of alkenes or alkynes, not carbonyl groups.
• $\mathrm{LiAlH}{}_4/\mathrm{\Delta }$ reduces carbonyl groups to alcohols ($-\mathrm{OH}$), not alkanes.
• $\mathrm{Pd}/\mathrm{H}{}_2/\mathrm{\Delta }$ is typically used for hydrogenation of alkenes or alkynes, not carbonyl groups.