Write in detail about the hydrogenation of unsaturated hydrocarbons.

(N/A) Definition of Hydrogenation: Dihydrogen gas $(H_2)$ adds to alkenes and alkynes in the presence of finely divided catalysts like platinum $(Pt)$,palladium $(Pd)$,or nickel $(Ni)$ to form alkanes. This process is called hydrogenation.
Work of catalyst: These metals adsorb dihydrogen gas on their surfaces and activate the hydrogen-hydrogen bond. Platinum and palladium catalyze the reaction at room temperature,but relatively higher temperature and pressure are required with nickel catalysts.
Examples of hydrogenation reactions:
$i$. $CH_2=CH_2 + H_2 \xrightarrow{Pt/Pd \text{ or } Ni, \Delta} CH_3-CH_3$ (Ethene $\rightarrow$ Ethane)
$ii$. $CH_3-CH=CH_2 + H_2 \xrightarrow{Pt/Pd \text{ or } Ni, \Delta} CH_3-CH_2-CH_3$ (Propene $\rightarrow$ Propane)
$iii$. $CH_3-C \equiv CH + 2H_2 \xrightarrow{Pt/Pd \text{ or } Ni, \Delta} CH_3-CH_2-CH_3$ (Propyne $\rightarrow$ Propane)