When acetaldehyde undergoes reaction with $Zn-Hg/HCl$, the product obtained is 

When acetaldehyde undergoes reduction reaction with $Zn-Hg/HCl$ in presence of $Hg$ in acidic condition then Ethane is obtained along with water molecule. 

$\underset{\mathrm{Acetaldehyde}}{{\mathrm{CH}}_3\mathrm{CHO}}+\underset{\mathrm{Proton}}{4{\mathrm{H}}^{+} }\underset{\mathrm{Conc}.\mathrm{HCl}}{\overset{ \mathrm{Zn}-\mathrm{Hg} }{\to }} \underset{\mathrm{Ethane}}{{\mathrm{CH}}_3{\mathrm{CH}}_3}+{\mathrm{H}}_2\mathrm{O} .$

Hence, the correct answer is option (B) ethane.