Explanation

(c)
Methane cannot be produced by Wurtz reaction, Kolbe’s electrolytic method and reduction with $H_{2}$because, it has one carbon atom.
Pure methane can be produced by the decarboxylation of sodium acetate.
$CH_{3}COONa + NaOH\overset{CaO\ \ }{\rightarrow}CH_{4} + Na_{2}CO_{3}$
Soda lime methane