"(/ˈflʊəriːn/, /ˈflʊərɪn/, or /ˈflɔrʔ/)" I have serious doubts that the third pronunciation is correct. Where did the second syllable go?
"It is a yellow or brown gaseous halogen, chemically similar and even more reactive and dangerous than chlorine gas, known for its poisonness, being one of the strongest oxidants known." This sentence tries, with little success, to cram several unrelated ideas into one sentence. I suggest splitting it into smaller sentences.
"Fluorine has the highest electronegativity of all elements, remaining the only chemical element not to be oxidized to form any positive ion by other chemicals." What does it mean to say that fluorine is "remaining the only chemical element..." ? Did the other elements go on strike? I suggest using a better verb.
It is not necessary to use {{!}} to pipe links. [[flux (metallurgy){{!}}flux]] should be replaced with [[flux (metallurgy)|flux]] in every case. See this edit for an example.
"In 1986, it was finally shown that fluorine can be produced without electrolysis, but this isn't used widespread." This leaves the reader wondering "What was that other method?", and the phrasing at the end is awkward. Suggested rewrite: "In 1986, it was finally shown that fluorine can be produced chemically, though electrolysis is still the most widespread production method."
"Its electronegativity and small atomic radius give unique properties to many of its compounds, such as the volatility of uranium hexafluoride, which is a rely for the enrichment of uranium, unusual strength of carbon–fluorine bond, which led to uses of fluorocarbons, such as teflon, and which led to its most of its uses, including dental one, where it strengthens tooth enamel." The length of this sentence and the abundance of commas contained therein make it difficult to determine what is being explained. Also, "rely" is a verb, not a noun.
There are several areas in need of additional references: Chemical characteristics, Compounds, Isotopes, the first and last paragraphs of history, Industrial, etc.
One helpful tidbit: every piece of information in a Wikipedia article should be verifiable through the use of references. This does not mean that every single sentence must be followed by a footnote, but a good rule of thumb is that every paragraph should end with a footnote.
"Fluorine has a density of 1.695 grams per liter and mass of 37.997 u per molecule, which makes fluorine about 1.3 times as dense as air." I assume this is referring to F2, not just F. If that's the case, I would suggest replacing "fluorine" with "fluorine gas" in the highlighted sentence.
"Fluorine can be detected in very small amounts, as low as a part per fifty millions, which means that the gas can be detected and avoided in case it leaks into a room." This sentence, which I pulled from Physical characteristics would be better suited for the Precautions section.
"Also, transactinides are not known to be oxidized by fluorine due to hardness of their receiving and no attempt was made, but all are highly likely to." I think I have an idea of what you're trying to say, so here's my attempt at rewriting it: "No attempt has been made to oxidize the transactinides with fluorine due to their instability, though such an oxidation would be possible in theory."
