The Wurtz reaction involves the coupling of two alkyl halides in the presence of sodium metal, leading to the formation of a higher alkane:
\[
\text{R-X} + \text{R-X} \xrightarrow{\text{Na}} \text{R-R} + 2 \text{NaX}
\]
In the case of methane (CH$_4$), since there is no carbon-carbon bond available in a single methyl group (CH$_3$), methane cannot be formed through the Wurtz reaction.
Thus, the product that is not possible is Methane.