Final answer:
a) Sulfur, being above selenium in the periodic table and in the same group, has the lowest electron affinity among the choices provided, due to the trend of decreasing electron affinity down the group.
Step-by-step explanation:
The element with the lowest electron affinity out of the options given (sulfur, selenium, bromine, chlorine) is sulfur. This is because, in general, electron affinities become less negative as we proceed down a group in the periodic table. Sulfur (S) is above selenium (Se) in the periodic table. While the trend across a period is for electron affinity to increase, since sulfur and selenium are in the same group, the trend going down the group is the dominant factor in this case. Therefore, sulfur will have a less negative electron affinity compared to selenium. Additionally, both chlorine (Cl) and bromine (Br) are halogens, and halogens are known to have high electron affinities, with chlorine having one of the most negative values.