Which of the following reactions is used to prepare hydrocarbons with an even number of carbon atoms?
$i.$ Wurtz reaction
$ii.$ Decarboxylation reaction
$iii.$ Kolbe's electrolysis
$iv.$ Reduction
$v.$ Hydrogenation

(I AND III) $i.$ Wurtz reaction and $iii.$ Kolbe's electrolysis are specifically used to prepare alkanes with an even number of carbon atoms.
In the Wurtz reaction,two alkyl halides couple to form a symmetric alkane $(2R-X + 2Na \rightarrow R-R + 2NaX)$.
In Kolbe's electrolysis,the electrolysis of sodium or potassium salts of carboxylic acids yields alkanes with an even number of carbon atoms $(2RCOOK + 2H_2O \rightarrow R-R + 2CO_2 + H_2 + 2KOH)$.