Here's why:

* Electronegativity: Francium has the lowest electronegativity of all elements, meaning it has a strong tendency to lose electrons and form positive ions.

* Ionization Energy: It has a very low ionization energy, making it easy to remove an electron.

* Position on the Periodic Table: Francium is located in Group 1 (alkali metals) of the periodic table. Elements in this group are known for their high reactivity.

Important Note: Francium is extremely rare and radioactive. Due to its radioactivity and short half-life, it is difficult to study its reactivity in detail.