What happens when 2-bromopentane reacts with alcoholic KOH?

Trans-2-pentene

The correct answer is option 2. trans-2-pentene.

When 2-bromopentane is treated with alcoholic KOH, it undergoes an \(E_2\) elimination reaction. This reaction removes a hydrogen atom and a bromine atom from the 2-position of 2-bromopentane, forming trans-2-pentene.

The other options are incorrect. Option (1) cis-2-pentene, is not formed because the elimination reaction is reversible, and the more stable trans-isomer is favored. Option (3) 1-pentene, is not formed because the bromine atom is not bonded to the 1-position of 2-bromopentane. Option (4) none of the above, is incorrect because trans-2-pentene is the major product of the reaction.