Q.Ethylidene chloride on treatment with aqueous KOH gives a) acetaldehyde b) ethylene glycol c) formaldehyde d) glyoxal

Poly halogen compounds carry two or more halogens, and the two commonest dihalide classes are distinguished purely by WHERE the two halogens sit on the carbon skeleton. gem-Dihalides ('geminal', same carbon): both halogens on ONE carbon, e.g. CH3-CHCl2 (ethylidene chloride/dichloride, 1,1-dichloroethane), made either from acetaldehyde + PCl5, or by adding HCl twice to acetylene via the vinyl chloride intermediate. vic-Dihalides ('vicinal', neighbouring carbons): the two halogens on ADJACENT carbons, e.g. ClCH2-CH2Cl (ethylene dichloride, 1,2-dichloroethane), made either by adding Cl2 directly to ethylene, or from ethylene glycol + PCl5/HCl. The single most exam-tested fact about this pair is how to tell them apart CHEMICALLY: both hydrolyse with aqueous NaOH/KOH, but a gem-dihalide gives an unstable geminal diol that collapses (loses water) to an ALDEHYDE OR KETONE, while a vic-dihalide gives a sta …