In the light (no pun intended!) of kriggy's suggestion, consider the first reaction (cyclohexene + Br2 + heat/UV light):
What product(s) would be expected to be formed if 1-deuteriocyclohexene had been used as starting material instead of (unlabeled) cyclohexene?
Then, consider the second reaction (para-nitroethylbenzene + Br2 + heat/UV light):
Would you expect alpha-bromination to occur faster, slower or at about the same rate if para-methoxyethylbenzene had been used as starting material instead of para-nitroethylbenzene?