Fluorine does not occur in the free state in nature because

Analyze the question: The question asks why fluorine is never found as a free element (F₂) in nature. The answer must be linked to its chemical behaviour.

Explain the concept: Fluorine is the most electronegative and most reactive of all the elements. Two things explain this:

• It has 7 valence electrons (configuration 2, 7), so it strongly attracts one more electron to complete its octet.
• Its atoms are very small, and the F-F bond is weak because of repulsion between the lone pairs on the two atoms. The molecule therefore splits easily and the atoms react readily.

Because of this, fluorine reacts with almost every other element, including some noble gases such as xenon, and with water, glass and metals. Any free fluorine would quickly combine with other substances. It is therefore found only in compounds, for example:

• Fluorspar (calcium fluoride, CaF₂)
• Cryolite (Na₃AlF₆)
• Fluorapatite

Check each option:

• A. It is a poisonous gas. Fluorine is toxic, but toxicity does not stop an element from occurring free. Poisonous substances can exist uncombined. This is not the reason.
• B. It belongs to the halogen family. This is only a classification. Iodine and chlorine are also halogens, but the reason a group member is not found free is its reactivity, not its membership of the group.
• C. It is inert. This is false. Fluorine is the opposite of inert. Inert elements, such as the noble gases, do occur free.
• D. Of its high reactivity. Correct. Fluorine combines readily with other elements, so it exists only in compounds.

Answer: D

Tip: In "why is element X not found free in nature?" questions, the answer is almost always high reactivity. This applies to fluorine, sodium, potassium and calcium. Elements that are found free are the unreactive ones, such as gold, platinum and the noble gases.