One of these elements is frequently used to detect starch, in the presence of which that element turns dark blue.
Along with magnesium, a member of this group of elements is found in Grignard reagents. One of these elements is frequently used to detect starch, in the presence of which that element turns dark blue. This group also contains the last naturally occurring element to be discovered. That element is the only one of the group to not naturally occur in diatomic form. For 10 points, give the name for group seventeen elements, which include astatine, iodine, and chlorine.
Along with magnesium, a member of this group of elements is found in Grignard reagents.
{halogens} [or Group 17 before mentioned; or {Group} 7a]