Answer
The but-1-ene $-->$ 1-bromobutane. It is free radical addition of HBr.
Work Step by Step
Draw the skeletal structures of the given compound names. In this one, it can be seen that the bromine is added to the least substituted carbon on the double bond. Thus, it can be concluded that the synthetic conversion that it went through is free radical addition of HBr. This addition needs peroxide as a reagent. In presence of peroxides, the halogen is always added to the least substituted carbon on the double bond.
