Fluorine

A non-metallic halogen — the most electronegative element and the strongest oxidising agent among them. With chemical symbol F and atomic number 9, it forms a pungent, pale-yellow gas or liquid. Fluoride occurs naturally in bone and teeth; chronic excess can cause skeletal fluorosis, while inadequate intake is linked to dental caries. It is used to manufacture fluorides. Its extreme reactivity makes elemental fluorine a laboratory and industrial curiosity rather than a food substance; dietary exposure is essentially to fluoride ion. Bone and teeth concentrate fluoride, where moderate levels strengthen enamel; chronic excess is harmful, and fluorosis is endemic in regions with high-fluoride groundwater.