Fluorine is the most reactive element of all in Group 7.
You can see the trend in reactivity if you react the halogens with iron wool.
|Halogen||Reaction with iron wool|
|Fluorine||Reacts with almost anything instantly. Very few scientists handle fluorine because it is so dangerous.|
|Chlorine||Reacts with heated iron wool very quickly.|
|Bromine||Has to be warmed and the iron wool heated. The reaction is faster.|
|Iodine||Has to be heated strongly and so does the iron wool. The reaction is slow.|