Step 1: What is Milk of Magnesia?
Milk of Magnesia is a well-known over-the-counter product used as both an antacid and a laxative. It appears as a milky-white aqueous suspension, which is where it gets its name.
Step 2: Identify its chemical composition.
Milk of Magnesia is an aqueous suspension of magnesium hydroxide, Mg(OH)2. Because Mg(OH)2 is sparingly soluble in water, it forms a white milk-like suspension rather than a clear solution.
Step 3: Evaluate each option.
Magnesium Carbonate (Option 1): MgCO3 is used as an antacid but is NOT Milk of Magnesia. Magnesium Trisilicate (Option 3): Mg2Si3O8 is another antacid but is slow-acting and also NOT Milk of Magnesia. Magnesium Sulphate (Option 4): MgSO4 is Epsom salt, used as a laxative in larger doses, but NOT Milk of Magnesia.
Step 4: Why Magnesium Hydroxide?
Mg(OH)2 neutralizes stomach acid: Mg(OH)2 + 2HCl gives MgCl2 + 2H2O. Its low solubility keeps it in suspension and reduces systemic absorption, making it safer than sodium bicarbonate as an antacid.
Step 5: Confirm the answer.
Milk of Magnesia = Magnesium Hydroxide [Mg(OH)2]. This is a basic inorganic pharmaceutical chemistry fact.
Answer: Option (2) — Magnesium Hydroxide