As we go down a group the reactivity of non-metals decrease.
This is because :
(a) How does the chemical reactivity of alkali metals vary on going down in group 1 of the periodic table?
(b) How does the chemical reactivity of the halogens vary on going down in group 17 of the periodic table?
Which is the most reactive nonmetal?
Metallic reactivity decreases down the group.