Question

observe the modern periodic table and explain the gradation in reactivity of halogen family

Answer 1

$\huge\color{green}{Hello}$

The reactivity of halogens decreases down the group. Reactivity of halogens means the tendency of gaining electrons to complete their octet. As the size of halogens increase down the group, the tendency to gain electrons decrease. That's why reactivity of halogens decreases.

Also note that tendency to gain electrons is measured by electron gain enthalpy (∆Eg). Down the group ∆Eg decreases as size increases. Hence reactivity of halogens decreases.