Iodine ingested iodine and retain it for periods longer than this isotope's radiological half-life of eight days. For this reason, people at risk of exposure to environmental radioactive iodine (iodine-131) in fallout may be instructed to take non-radioactive potassium iodide tablets. The typical adult dose is one 130 mg tablet per 24 hours, supplying 100 mg (100,000 micrograms) of ionic iodine. (The typical daily dose of iodine for normal health is of order 100 micrograms; see "Dietary Intake" below.) Ingestion of this large dose of non-radioactive iodine minimises the uptake of radioactive iodine by the thyroid gland. As an element with
Iodine the iodyl cation, [IO], and is reduced by concentrated sulfuric acids to iodosyl salts involving [IO]. It may be fluorinated by fluorine, bromine trifluoride, sulfur tetrafluoride, or chloryl fluoride, resulting iodine pentafluoride, which also reacts with iodine pentoxide, giving iodine(V) oxyfluoride, IOF. A few other less stable oxides are known, notably IO and IO; their structures have not been determined, but reasonable guesses are I(IO) and [IO][IO] respectively. More important are the four oxoacids: hypoiodous acid (HIO), iodous acid (HIO), iodic acid (HIO), and periodic acid (HIO or HIO). When iodine dissolves in aqueous solution, the following reactions occur: Hypoiodous