Which one among the following is known as Milk of Magnesia?
- (a)Magnesium bicarbonate
- (b)Magnesium carbonate
- (c)Magnesium sulphate
- (d)Magnesium hydroxide
Correct — D, magnesium hydroxide. Milk of Magnesia is a white aqueous suspension of magnesium hydroxide, Mg(OH)₂. Because it is a mild, only slightly soluble base, it neutralises excess hydrochloric acid in the stomach, so it is used as an antacid and, in larger doses, as a laxative.
- (a)Magnesium bicarbonate — Magnesium bicarbonate exists mainly in solution and is not the substance sold as Milk of Magnesia, which is the hydroxide.
- (b)Magnesium carbonate — Magnesium carbonate is a separate white solid (used as a drying agent and mild antacid), but the specific preparation called Milk of Magnesia is the hydroxide, not the carbonate.
- (c)Magnesium sulphate — Magnesium sulphate is Epsom salt, used as a purgative and in bath salts — a different magnesium compound, not Milk of Magnesia.
Milk of Magnesia is the common name for a suspension of magnesium hydroxide in water. Mg(OH)₂ is a weak, only slightly soluble base, gentle enough to swallow: it neutralises stomach acid (HCl) without being caustic, giving relief from acidity and indigestion.
Read past the other magnesium-compound distractors to the specific named preparation. Epsom salt is the sulphate, and the carbonate and bicarbonate are different compounds; the milky white antacid suspension called Milk of Magnesia is specifically magnesium hydroxide.
- Milk of Magnesia is an aqueous suspension of magnesium hydroxide, Mg(OH)₂.
- As a mild base it neutralises excess stomach acid: Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O.
- It acts as an antacid at small doses and as a laxative at larger doses.
- Epsom salt is magnesium sulphate (MgSO₄·7H₂O), a different magnesium compound used as a purgative.
- Confusing Milk of Magnesia (hydroxide) with Epsom salt (sulphate).
- Assuming a strong base is used — Mg(OH)₂ is deliberately weak and insoluble so that it is safe to ingest.
- Mixing up magnesium carbonate and magnesium hydroxide.
NDA/UPSC ask for the chemical name behind a common name (Milk of Magnesia, Epsom salt) or which compound acts as an antacid.
No directly related past PYQ was found.
- practice — not a real PYQ
Epsom salt, used as a purgative, is chemically
- (a)magnesium hydroxide
- (b)magnesium sulphate
- (c)magnesium carbonate
- (d)magnesium chloride
Answer(b) magnesium sulphate — MgSO₄·7H₂O is Epsom salt, distinct from the hydroxide in Milk of Magnesia.
- practice — not a real PYQ
An antacid taken to relieve acidity works by
- (a)oxidising stomach acid
- (b)neutralising excess stomach acid
- (c)increasing stomach acid
- (d)precipitating enzymes
Answer(b) neutralising excess stomach acid — a mild base such as Mg(OH)₂ reacts with the HCl.