For 10 points, name this sublimation-prone element found on the periodic table below bromine.
A compound containing a heteroatom of this element reacts with DFP in a one-step synthesis of sarin gas. Reagents containing this element that can oxidize primary alcohols to aldehydes include DMP and IBX, which reacts through a "hypervalent twisting" mechanism. In two similar reactions employing silver salts, a cyclic cation of this element is opened by nucleophilic attack to synthesize vicinal diols. Under basic conditions, a yellow solid containing three atoms of this element will precipitate after three successive (*) enolizations, giving a positive result in a test for methyl ketones. The Prévost and Woodward hydroxylations employ the diatomic form of this element, which is a common indicator for starch. This element's radical substitution is too endothermic to halogenate alkanes. For 10 points, name this sublimation-prone element found on the periodic table below bromine.
A compound containing a heteroatom of this element reacts with DFP in a one-step synthesis of sarin gas.
iodine [accept I or I2; accept iodide]