For 10 points, name this group of elements that includes bromine, iodine, chlorine, and fluorine.
One element in this group forms Grignard (GRIN-yurd) reagents with magnesium. Another element in this group is used in a test to detect starches in a solution; that test is named for Lugol (LOO-gul). That element from this group is also used in a tincture to disinfect skin. Two of these elements combine with carbon to form a series of compounds that are a major threat to the ozone layer. For 10 points, name this group of elements that includes bromine, iodine, chlorine, and fluorine.
One element in this group forms Grignard (GRIN-yurd) reagents with magnesium.
{halogens} [or Group 17; or Group {VIIA}]