Chlorine (Cl) is the most reactive non-metal. Option C
Group 17 (Group VIIA) of the periodic table, referred to as the halogens, includes chlorine. Since chlorine is a halogen—a highly reactive non-metal—it easily builds compounds by obtaining an electron to complete an outer electron shell.
On the other hand, under normal circumstances, noble gases like argon (Ar) and helium (He) are typically inert or unreactive. As a metalloid, silicon (Si) is less reactive than chlorine as we can see above.