Fluorine is the most reactive Halogen, and is in fact more reactive than most elements in the periodic table as far as I'm aware (Except the badass radioactive ones).
|Fluorine is too reactive to be put in glass, this is just an imitation of what Fluorine gas looks like.|
Fluorine is a pain to transport, because it tends to react with whatever you put it in.
Fluorine is an oxidising agent with an insane charge density.
Tends to chill around in nature as Calcium Fluoride.
|Calcium Fluoride physically looks much like Titanium(IV)Oxide.|
CaF + H2SO4 --> CaSO4 + 2HF
Uses include Toothpaste, HCFC making and facial surgery.
Bromine is another halogen, named after "Bromos", greek for "Stench".
Bromine can only be transported in lead tanks, or similar, which are very heavy. Therefore, it's often transported by rail.
Uses include Flame retardants (TBBA), Pharmaceutics, Pesticides, Dyes, Fumigants like Bromoethane.