One element in this group is capable of forming compounds with the relatively inert Xenon and Radon.  
They can sometimes be used to increase membrane permeability, while their "pseudo" variety usually features bond formation with a cyanide ion.  One element in this group is capable of forming compounds with the relatively inert Xenon and Radon.  The heaviest discovered member of this group likely accumulates in the thyroid gland like another member of the group, and is named Astatine.  Because they lack an eighth electron, they tend to be highly reactive and cannot be found in their pure form in nature.  For 10 points, identify this group of elements containing iodine, fluorine and chlorine, all of which produce salts.
They can sometimes be used to increase membrane permeability, while their "pseudo" variety usually features bond formation with a cyanide ion.  
{Halogens} (also accept {Group VIIA} or {Group 17})