Correct matching is Benzene - (4n+2)π electrons Ethylene - Mustard gas Acetaldehyde - Silver mirror Chloroform - Phosgene Benzene has 6π electrons, i.e., it follows Huckel rule (4n+2)π electrons. Ethylene reacts with S2Cl2 to give mustard gas (war gas). Acetaldehyde gives positive silver mirror test with Tollen's reagent and chloroform on oxidation gives phosgene (poisonous gas).