The alkyl halide that forms the alkene shown as the only product in an elimination reaction is bromomethyl cyclohexane.
An elimination reaction is a reaction in which two atoms are removed to create a double bond. Elimination reaction is a type of reaction that is common to alkyl halides.
In this reaction, a hydrogen atom and a halogen atom are both removed to yield a double bond. The structure of the product depends on the structure of the reactant alkyl halide.
Bromomethylcyclohexane shown in the image attached yields the alkene product in the image attached as the only product when it undergoes elimination reaction.