Multiple choice general knowledge science & technology Magnesium Hydroxide milk of magnesia Laxative Both a & b None of the above Reveal answer Fill a bubble to check yourself C Correct answer Explanation Magnesium hydroxide is the active ingredient in milk of magnesia, which is used as a laxative and antacid. Therefore, both A and B are correct - magnesium hydroxide IS milk of magnesia, and it IS a laxative.