Answer:

on the benzene ring, of the two substituents, bromine is the more reactive. It is an ortho-para deactivator, so incoming molecules of NO2 will substitute in either the ortho or para positions relative to the bromine in the ring. Since para (position 4) is the furthest you can get from the bromine, it is the most stable, because there will be less of a chance of the elements repelling each other and experiencing strain associated with steric hindrance.