5) BF 3 and 1) CF 3+ these species have only 6 electrons in there outer most shell and rest all the species will have 8 electrons in there outermost shell... hence they are odd one out. Solution 5) BF 3 and 1) CF 3+ these species have only 6 electrons in there outer most shell and rest all the species will have 8 electrons in there outermost shell... hence they are odd one out..