Final answer:
Fluorine is the most electronegative halogen atom, with the highest electronegativity value of 3.98, making it more electronegative than bromine, chlorine, and iodine.
Step-by-step explanation:
The halogen atom that is most electronegative among the listed options is fluorine. Halogens are elements found in Group 17 (Group VII) of the periodic table and include fluorine, chlorine, bromine, and iodine. They have an electron configuration of ns²np⁵ in their outer shell, indicating that they have seven electrons in their valence shell and are one electron short of a full octet, which makes them highly reactive and able to form negative ions by gaining an electron.
Fluorine, with a Pauling electronegativity value of 3.98, is the most electronegative element on the periodic table. Electronegativity generally increases across the periodic table from left to right and decreases down a group, meaning that the elements at the top right of the periodic table (excluding noble gases) tend to have the highest electronegativity. Therefore, fluorine, being at the top of the halogen group, is more electronegative than other halogens such as chlorine, bromine, and iodine.