Correct answer: Ar
Explanation:
Argon (Ar) is a chemical element that belongs to Group 18 of the modern periodic table, also known as the noble gases. These elements are characterized by their full outer electron shells, making them chemically inert or unreactive.
On the other hand:
- \(F_2\) (Fluorine),
- \(Cl_2\) (Chlorine), and
- \(I_2\) (Iodine)
are all halogens (Group 17 elements), and they are not noble gases.