Which of the following alkyl halides yields exactly four isomeric alkenes (including stereoisomers) upon dehydrohalogenation with alcoholic KOH?

Step-by-step solution

Dehydrohalogenation of alkyl halides follows the E2 mechanism. The total number of isomeric alkenes includes both structural and geometrical (cis/trans) isomers. Let us evaluate each option: 1) 2-Bromohexane: Elimination can occur at C1 or C3. This yields hex-1-ene (no stereoisomers) and hex-2-ene (exists as cis and trans). Total = 1 + 2 = 3 isomers. 2) 2-Bromopentane: Elimination at C1 or C3 yields pent-1-ene (no stereoisomers) and pent-2-ene (exists as cis and trans). Total = 1 + 2 = 3 isomers. 3) 3-Bromohexane: