How many of the following compounds exhibit geometrical isomerism? (I) But-2-ene (II) 1,1-Dichloroethene (III) 1,3-Dimethylcyclopentane (IV) 2-Methylbut-2-ene (V) 1,2-Dimethylcyclohexane

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For geometrical isomerism (GI) in alkenes, each carbon atom of the double bond must be bonded to two different atoms or groups. For GI in cycloalkanes, at least two sp ^3 hybridized ring carbons must each be bonded to two different atoms or groups. (I) But-2-ene: CH₃-CH=CH-CH₃ . Each double-bonded carbon is attached to a hydrogen atom and a methyl group. It exhibits GI. (II) 1,1-Dichloroethene: CCl₂=CH₂ . One double-bonded carbon is attached to two identical chlorine atoms. It does not exhibit GI. (III) 1,3-Dimethy