The Wurtz reaction couples two molecules of an alkyl halide using sodium metal in dry ether to form a symmetrical alkane containing twice the carbon atoms of the alkyl group. The general reaction is $2R-X+2Na\to R-R+2NaX$. With bromoethane, $C{H}_{3}C{H}_{2}Br$, each ethyl fragment has two carbons, so coupling two of them gives a four-carbon chain, $C{H}_{3}C{H}_2-C{H}_{2}C{H}_3$, which is n-butane. Ethane is wrong because it would require simple reduction of one ethyl halide without coupling, which is not the Wurtz outcome. Propane has three carbons, an odd number that cannot arise from coupling two identical two-carbon units, so it is incorrect. n-Hexane has six carbons and would need coupling of two propyl groups, not ethyl groups, so it does not apply here. A practical limitation of the Wurtz reaction is that it is best suited to making symmetrical alkanes, because using two different alkyl halides produces a mixture of three coupling products that is difficult to separate. The reaction is thought to proceed through an organosodium intermediate that behaves as a carbanion and displaces halide from a second alkyl halide molecule. This is the standard NCERT preparation of symmetrical alkanes via the Wurtz reaction. A consistency check: coupling two identical fragments must double the carbon count, and two carbons doubled gives four, matching n-butane exactly.