Here's why:

* Electronegativity is the tendency of an atom to attract electrons towards itself within a chemical bond.

* Electronegativity generally increases across a period (from left to right) and decreases down a group (from top to bottom) in the periodic table.

* Chlorine and iodine are both in Group 17 (halogens), but chlorine is higher up the group than iodine.

Therefore, chlorine has a higher electronegativity than iodine.