When ethyl bromide is heated with sodium in dry ether solvent, the alkane obtained is

Usually in Wurtz reaction, the product alkanes consists of double the number of carbon atoms with respect to reactant. So the given starting material is ethyl bromide having two carbon atoms which upon heating with sodium in ether produces butane as product with  four number of carbon atoms and sodium bromide as side product.

$2C_2{H}_{5}Br+2Na\to C_2{H}_5-C_2{H}_5+2NaBr$