# fluorine

/ˈfɫɔˌɹin/ (US) · /flˈɔːɹiːn/ (UK) · CEFR C1 · Noun

Source: https://englishreference.com/word/fluorine
Updated: 2026-05-30

## Definition

a very active, greenish-yellow gas that is the most reactive of all the chemical elements. It is used to make things like toothpaste and plastic.

For teachers: a highly reactive, pale yellow-green diatomic gas with the atomic number 9. It is the most electronegative and reactive of all the chemical elements, typically existing in a gaseous state at standard temperature and pressure.

## Examples

- Fluorine is used to make certain types of plastic.
- The chemist handled the fluorine gas with extreme care because it reacts violently with almost any other substance.
- As the lightest halogen, fluorine exhibits unique properties that make it essential for the synthesis of pharmaceuticals and high-performance materials, though its extreme reactivity requires specialized containment.

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