If f is a reactive nonmetal, which other element or elements shown here do you expect to also be a reactive nonmetal?

You did not include the list but F is fluorine. The first halogen.

So, you can expect that the other members of the same group (halogens, column 17 of the periodic table) exhibit similar chemical behavior (reactivity).

So, I am sure your list contains one or more of theses elements: Cl (chlorine), Br (bromine), and I (iodine).

All of them you can expect to also be reactive non metal.