Final answer:
Iodine has the least electron affinity among the halogens due to its position further down the group, resulting in a weaker attraction between the added electron and the nucleus compared to fluorine, chlorine, and bromine.
Step-by-step explanation:
The halogen with the least electron affinity is iodine. Electron affinity generally decreases as you move down the group in the periodic table. Therefore, among the given options, which include fluorine, chlorine, bromine, and iodine, it is iodine that has the least electron affinity. This is because, as atomic number increases, the additional electron enters an orbital that is farther from the nucleus and this weaker attraction leads to a lower electron affinity. Iodine is the least reactive halogen, acting as the weakest oxidizing agent compared to its counterparts. While substances like fluorine and chlorine have intensely negative electron affinities and readily form anions, iodine requires heating to react with metals and does not easily oxidize other halide ions.