The best replacement for fluorine is fluoride.

The best alternatives to fluorine are rated as following:
★★★★★  fluoride
★★★  chlorine
★★  fluorine
★★  bromine
★  chlorine more reactive
  weborb
  francium
  neon

Your alternative for fluorine is not listed? Suggest!
Speaking about fluorine, one probably shouldn't forget about sodium bromide.

Other search terms related to fluorine and their ratings are:
★★★★★ sodium bromide
★★★★★ iron wool
★★★★ hydrogen
★ methane
You have in mind a companion for fluorine and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of fluorine in all years. Click on graph for more.
fluorine
fluoride
chlorine