Concept:The reaction is a Wurtz reaction, where two identical alkyl halides couple in presence of dry ether and sodium metal.Explanation:The general Wurtz reaction is:2R−X+2Nadry ether​R−R+2NaXThe given product is 3,4-diethyl-3,4-dimethylhexane.Its symmetrical structure is:CH3​CH2​−C(CH3​)(C2​H5​)−C(CH3​)(C2​H5​)−CH2​CH3​In Wurtz reaction, the new bond forms between the two carbons that originally carried halogen atoms.So, break the central bond between C-3 and C-4 to get two identical halves.Each half has the structure:CH3​CH2​−C(Cl)(CH3​)−CH2​CH3​The longest chain contains five carbons, with chlorine and methyl group at C-3.Hence, the substrate is 3-chloro-3-methylpentane.Answer:Option C: 3-chloro-3-methylpentane.