Which of the following is an allylic halide?

Halides known as allylic halides are those in which a halogen atom is joined to a carbon atom that has undergone $s{p}^3$ hybridization next to a carbon-carbon double bond (C=C). Allylic halides have the following general chemical structure:

$C{H}_2=CH-C{H}_2-X$

X here can be any halogen atom.
Let's now sketch the composition of each compound to identify the allylic halide. - 3-bromo -2-methylpropene

- 3-bromobut-1-ene:

- 3-bromopent-2-ene

 - 4-bromobut-1-ene

The structures of the aforementioned compounds show that bromine is joined to the $s{p}^3$ hybridised carbon atom, which is adjacent to the carbon-carbon double bond or $s{p}^2$ hybridised carbon, in 3-bromo-2-methylpropene and 3-bromobut-1-ene. Thus, the allylic halides 3-bromo-2-methylpropene and 3-bromobut-1-ene are both present.