It’s c I believe because it says 209 years to complete an orbit so hint yourself ?.....
Answer:
Iron's atomic number is 26
Explanation:
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.
