The Wurtz reaction between methyl chloride and sodium metal in presence of dry ether can be written as :
$2CH_3Cl+2Na \ce{ ->[{\text{Dry ether}}] } \underset{\text{Ethane}}{CH_{3} �CH_{3}}+2NaCl$
$\Rightarrow 2$ moles of sodium metal reacts to give 1 mole of ethane.
Also,
1 mole of Na metal $=23 \,g$
$\therefore 2$ moles of Na metal $=23 \times 2=46 \,g$
Thus, $46 \,g$ of sodium is required to prepare one mole of ethane from methyl chloride by Wurtz reaction