IUPAC name of the following compound is:

The correct answer is Option (1) → 4-Bromopent-2-ene

In naming an alkene with a substituent, the parent chain is the longest chain containing the double bond, and it is numbered so that the double bond gets the lowest locant. The halogen is only a prefix, so it is numbered after the double bond has been placed.

The given compound is \( \ce{CH3-CH=CH-CH(Br)-CH3} \): a five-carbon chain (pent-) with one double bond (-ene).

• Numbering from the left, the double bond is between C2 and C3 and Br is on C4: locant of the double bond = 2.

• Numbering from the right, the double bond would be between C3 and C4 and Br on C2: locant of the double bond = 3.

The left-hand numbering wins, so the name is 4-bromopent-2-ene.