Task: Text Categorization
Input (English): A member of this group provides the counter-ion to an organomagnesium Grignard ("green-yard") reagent. Lugol's solution contains an element from this group that forms a complex with starch, turning it dark blue. Compounds that contain two members of this group and carbon are called freons and deplete the ozone layer. The only radioactive element in this group is the only one that does not exist in nature diatomically. The most [*] electronegative element in the periodic table is a member of this group and three of them can pair with hydrogen to form strong acids. For 10 points, name these elements that include astatine, bromine, iodine, chlorine, and fluorine.
Output (English): Science