This element is the heaviest stable member of the halogen group, and contains seven valence electrons in its outermost fifth shell. This halogen is the least abundant of the stable halogens, but attaches to organic compounds easily, which is why it is common as a radiocontrast material. This halogen is essential to hormones in the thyroid, and a lack of it can lead to intellectual deficiencies. For 10 points, name this halogen, which turns to a purple gas when sublimated, with atomic number 53 and chemical symbol "I."
A) Iodine
B) Chlorine
C) Fluorine
D) Bromine