Give the methods of preparation of alkanes. Write the general reactions.

(N/A) The important methods for the preparation of alkanes are as follows:
$(i)$ From unsaturated hydrocarbons (Hydrogenation):
$R-CH=CH_2 + H_2 \xrightarrow{Pt/Pd/Ni} R-CH_2-CH_3$
$R-C \equiv CH + 2H_2 \xrightarrow{Pt/Pd/Ni} R-CH_2-CH_3$
$(ii)$ From alkyl halides (Reduction):
$R-X + H_2 \xrightarrow{Zn + HCl \text{ (dil.)}} R-H + HX$
$(iii)$ Wurtz reaction:
$2R-X + 2Na \xrightarrow{\text{dry ether}} R-R + 2NaX$
$(iv)$ From carboxylic acids (Decarboxylation):
$R-COONa + NaOH \xrightarrow{CaO, \Delta} R-H + Na_2CO_3$
Soda lime is a mixture of $NaOH$ and $CaO$.