The Wurtz reaction couples two alkyl halide molecules using sodium metal in dry ether to build a longer, symmetrical alkane by joining the two alkyl fragments through a new carbon-carbon bond. Each bromoethane supplies an ethyl group of two carbons, so coupling two ethyl groups produces a four-carbon chain, namely n-butane, while the bromine and sodium combine as sodium bromide. Ethene is wrong because Wurtz forms a saturated alkane by C-C coupling, not an alkene by elimination. Propane is incorrect because it has three carbons, which cannot result from joining two identical two-carbon units. Hexane is wrong as six carbons would require coupling two propyl groups, not two ethyl groups. This is the standard NCERT method for preparing symmetrical alkanes with an even, doubled number of carbon atoms. Sanity check: two ethyl groups of two carbons each give 2 + 2 = 4 carbons, exactly matching n-butane as the coupled product.