Answer: -
The mechanism for Br production from NBS is shown in the attached file.
N-bromo succinimide is a reagent used to brominate. It is most commonly used in allylic bromination, where a hydrogen on a carbon adjacent to a double bond is replaced.
It is selective in nature, unaffecting the normal double bond as compared to only bromine.
It also has a low concentration of bromine as an added advantage.
