The IUPAC name of the compound is:

The correct answer is Option (2) → 3-bromo-2-methylbut-1-ene

To name an alkene with substituents by the IUPAC system:

• Choose the longest chain containing the C=C bond. This gives the parent name ending in -ene.

• Number the chain so that the double bond gets the lowest locant.

• Name halogens as prefixes (bromo, chloro) and alkyl groups as prefixes (methyl), and write all prefixes in alphabetical order.

The given compound is:

    \( \displaystyle \ce{CH2=C(CH3)-CH(Br)-CH3} \)

The longest chain containing the double bond has four carbon atoms, so the parent is butene. Numbering from the \( \ce{CH2} \)= end puts the double bond between C-1 and C-2. The methyl group is then on C-2 and the bromine on C-3. Bromo comes before methyl alphabetically.

So the name is 3-bromo-2-methylbut-1-ene.

NCERT (2026-27 edition):
Nomenclature – …