Compounds consisting of carbon and hydrogen are known as hydrocarbons.
(i) Saturated hydrocarbons : Alkanes $\left({\mathrm{C}}_{\mathit{n}}{\mathrm{H}}_{2\mathit{n}+2}\right)$ are the compounds of carbon which have single bond.
$\mathrm{H}-\underset{\underset{\mathrm{H}}{|}}{\overset{\stackrel{\mathrm{H}}{|}}{\mathrm{C}}}-\mathrm{H}$
(ii) Unsaturated hydrocarbons : The compounds of carbon having double bonds are alkene $\left({\mathrm{C}}_{\mathit{n}}{\mathrm{H}}_{2\mathit{n}}\right)$ and those having triple bonds are alkyne $\left({\mathrm{C}}_{\mathit{n}}{\mathrm{H}}_{2\mathit{n}-2}\right)$.
The reaction which converts unsaturated hydrocarbons to saturated hydrocarbons i.e. alkenes to alkane is known as hydrogenation reaction. It is used to obtain ghee from oil.