Fluorine (F), Chlorine (Cl) and Iodine (I) are all found in the same group on the Periodic Table because they have similar physical properties. Since they are all Halogens, they have 7 valence electrons in their outer shell. In order to get a total of 8, they naturally combine with elements of the same isotope (itself), so D comes close to being correct, but it's not the best answer choice.
