For 10 points, name this halogen used in the treatment of goiter.
Egyptian biochemist Fawzia Fahim studied the anti-tumor activities of a derivative of acetic acid with this element. A deficiency of this element can lead to Plummer's disease, and an excessive amount of it can lead to the paradoxical (**) WolffÂ–Chaikoff effect. An antisepttc containing this element and povidone is sold under the brand name Betadine. This element is found in Lugol's solution, and it is used as a (*) mordant in Gram staining. Kelp is a rich source of this element, which forms a dark blue complex in the presence of starch. For 10 points, name this halogen used in the treatment of goiter.
Egyptian biochemist Fawzia Fahim studied the anti-tumor activities of a derivative of acetic acid with this element.
iodine