What is a "Iodine"

What is a "Iodine"? This item is unfamiliar to many people, and here's the introduction to it:

Iodine periodic table no. 53, in the chemical elements in the periodic table in 5 periodic system Ⅶ A tribe is one of the halogen elements. In 1811, the French pharmacist, kutwa, first discovered the single iodine. Single iodine is violet black crystal, easy to sublimate, sublimation easy to be. Toxic and corrosive. The starch is blue and purple when it meets the starch. It is mainly used for medicine, dyestuff, iodine, test paper and iodine compound. Iodine is one of the essential micronutrients in the body. The total amount of iodine in healthy adults is 30 mg (20 ~ 50 mg), and the national standard for adding iodine to salt is 20 to 30 mg/kg.