The answer should be group 16. You can tell this because you know that X must be a negatively charged element due to the fact that it is in an ionic compound with iron. Iron is the metal (positively charged) so X must be negatively charged. Iron can have two charges: +2 or +3, so you know that that X must be -2 because it cancels in the first equation and in the second there are 2 irons. There is only one column with a negative 2 charge: group 16
