Why is fluorine more reactive than chlorine

Why is fluorine more reactive than chlorine?

A) Fluorine has more electrons than chlorine.
B) Fluorine has a smaller atomic radius than chlorine.
C) Chlorine has a higher atomic number than fluorine.
D) Fluorine has a higher density than chlorine.

Answer:

B) Fluorine has a smaller atomic radius than chlorine.

Why is fluorine more reactive than chlorine