Among the elements Iodine (I), Fluorine (F), Bromine (Br), and Chlorine (Cl), Fluorine (F) has the highest electron affinity. Electron affinity refers to the energy change that occurs when an atom gains an electron to form a negative ion.
Fluorine, being in Group 17 (or Group 7A) of the periodic table, has a very high electron affinity due to its small atomic size and strong nuclear charge. As a result, it strongly attracts additional electrons to fill its valence shell.
The electron affinity generally decreases as you move down Group 17 from Fluorine to Chlorine, Bromine, and Iodine. This is because the atomic size increases down the group, leading to weaker attractive forces between the nucleus and the added electron.
So, in summary, the elements in decreasing order of electron affinity are as follows: Fluorine (F) > Chlorine (Cl) > Bromine (Br) > Iodine (I)