<unk>  is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at 114 degrees Celsius, and boils to a violet gas at 184 degrees Celsius. The element was discovered by the French chemist Bernard Courtois in 1811, and was named two years later by Joseph Louis Gay-Lussac, after the Ancient Greek 'violet-coloured'.<unk>  occurs in many oxidation states, including<unk>  (I−), iodate (), and the various periodate anions. It is the least abundant of the stable halogens, being the sixty-first most abundant element. It is the heaviest essential mineral nutrient.<unk>  is essential in the synthesis of thyroid hormones.<unk>  deficiency affects about two billion people and is the leading preventable cause of intellectual disabilities. The dominant producers of<unk>  today are Chile and Japan.<unk>  and its compounds are primarily used in nutrition. Due to its high atomic number and ease of attachment to organic compounds, it has also found favour as a non-toxic radiocontrast material. Because of the specificity of its uptake by the human body, radioactive isotopes of<unk>  can also be used to treat thyroid cancer.<unk>  is also used as a catalyst in the industrial production of acetic acid and some polymers. It is on the World Health Organization's List of Essential Medicines.
Iodine
Lindane
Copper 
Chorus
Fluoride
Amine fluoride
Hydrogen fluoride
Sodium fluoride