The Clemmensen reduction involves the reduction of the carbonyl group ($>C=O$) of aldehydes and ketones to a methylene group ($-CH_2-$) on treatment with zinc amalgam and concentrated hydrochloric acid ($Zn-Hg/HCl$).

• Option 2 depicts the Wolff-Kishner reduction, which uses hydrazine ($NH_2NH_2$) and a strong base (like $C_2H_5ONa$ or $KOH$) in a high-boiling solvent (ethylene glycol).
• Option 3 depicts reduction using hydroiodic acid ($HI$) and Red Phosphorus, which is a powerful reducing method but not the Clemmensen reduction.
• Option 1, by elimination and matching the standard definition, corresponds to the reaction involving $Zn-Hg$ and $HCl$.