Which is larger Fe 2 plus or Fe 3 plus?

Fe3+ is smaller. Its ionic radius is 63 pm, while Fe2+ has an ionic radius of 77 pm. (For comparison, the Fe atom has a radius of 140 pm.) This is because the outermost electron in the 2+ ion is pulled off to form the 3+ ion. This outermost electron was the most weakly held. The remaining electrons are closer to the nucleus.