Write the IUPAC name of the following compound:
CH₂ = CHCH₂ Br [1]

As there are 3 carbons in the main chain, the name would have ‘prop’. Also due to the priority of double bond over halogen, numbering is done from the left end. We see –Br on the 3^rd carbon atom so the name would have a 3-bromo in the beginning and an –ene at the end as 1^st carbon atom is joined by a double bond with the second carbon atom. So, the IUPAC name is

3-bromopropene or 3-bromoprop-1-ene.