Multiple choice Which of the following will have deficiency defect? NaCI FeO KCI ZnO Reveal answer Fill a bubble to check yourself B Correct answer Explanation FeO (Ferrous oxide) is a classic example of a metal-deficient defect, where the ratio of iron to oxygen is less than 1:1 due to the presence of Fe(3+) ions replacing some Fe(2+) ions to maintain electrical neutrality.