Explain the gradation in reactivity of halogen family

The halogens is made up Fluorine, Bromine, Iodine and Astatine.

This group is made up of the most reactive elements on the periodic table. The behaviour of the halogens in this manner is because they have seven electrons in their outer shells. They would require just an electron to complete their octet.

Within the group, there is gradation in the reactivity of the elements. The oxidizing power decreases from top to down and reactivity follows this trend too.

Fluorine is the most reactive and Astatine is the least reactive.

Due to this, we find that the more powerful oxidizing halogen displaces a less powerful one from simple salts.

Fluorine is highly reactive due to its small atomic radius and high electronegativity. This trend progrades down the group.

Size and electronegativity increases down so also reactivity decreases.