Multiple choice Magnesia alba is obtained by the addition of ____________. MgCO3 and MgSO4.7H2O CaCO3 and H2O AgCl and HNO3 MgCl2 and MgO None of these Reveal answer Fill a bubble to check yourself A Correct answer Explanation This option is correct. Magnesia alba is a white substance, which is used in medicine as an antacid laxative and tooth powder, which is formulated as [Mg(CO3)x.Mg(OH)2]y.ZH2O.