Final answer:
Fluorine has the greatest electron affinity among the list of given atoms, which include iodine, nitrogen, sodium, sulfur, and arsenic, due to its high tendency to gain electrons to attain a full valence shell.
Step-by-step explanation:
Out of the given options, fluorine has the greatest electron affinity. Electron affinity refers to the amount of energy released when an electron is added to a neutral atom in the gaseous state to form an anion. In general, the elements with the highest electron affinities are found in the halogen group.
However, it is important to note that while one might expect the first element in a group to have the highest electron affinity, due to smaller atomic radii and therefore higher effective nuclear charge, this isn't always the case. For instance, chlorine has a higher electron affinity than fluorine, due to inter-electronic repulsions in the smaller 2p orbitals of fluorine. Even then, among the provided elements, fluorine has the highest tendency to gain an extra electron to achieve a full valence shell, reflecting that it has the greatest electron affinity among these choices.