Here's why:

* Reactivity of Halogens: Halogens become less reactive as you move down the group in the periodic table. This is due to decreasing electronegativity and increasing atomic size.

* Order of Reactivity: The order of reactivity for the halogens is:

* Fluorine (F) - Most reactive

* Chlorine (Cl) - Second most reactive

* Bromine (Br) - Third most reactive

* Iodine (I) - Fourth most reactive

* Astatine (At) - Least reactive

Let me know if you have any other questions!