Describe the preparation of alkanes from unsaturated hydrocarbons.

(N/A) The process of adding dihydrogen gas to alkenes and alkynes in the presence of finely divided catalysts like $Pt$,$Pd$,or $Ni$ to form alkanes is known as hydrogenation.
Catalytic Mechanism: These metals adsorb dihydrogen gas on their surfaces,which activates the $H-H$ bond. $Pt$ and $Pd$ catalyze the reaction at room temperature,whereas $Ni$ requires higher temperature and pressure.
Examples:
$(i)$ $CH_2=CH_2 + H_2 \xrightarrow{Pt/Pd \text{ or } Ni, \Delta} CH_3-CH_3$ (Ethene to Ethane)
$(ii)$ $CH_3-CH=CH_2 + H_2 \xrightarrow{Pt/Pd \text{ or } Ni, \Delta} CH_3-CH_2-CH_3$ (Propene to Propane)
$(iii)$ $CH_3-C \equiv CH + 2H_2 \xrightarrow{Pt/Pd \text{ or } Ni, \Delta} CH_3-CH_2-CH_3$ (Propyne to Propane)