Concept:Ethyne undergoes cyclic polymerization in the presence of hot, finely divided iron to form benzene, which is aromatic.Explanation:Three molecules of ethyne combine when passed through a hot iron tube.The reaction is: 3C2H2873K,FeC6H6.The product, benzene, has a ring structure with alternating single and double bonds.This benzene ring is the characteristic feature of aromatic compounds, not polymers, saturated hydrocarbons, or hydrated compounds.Answer:D. aromatic