Question

Assertion: Magnesium hydroxide is a better antacid than sodium hydrogen carbonate.
Reason: Magnesium hydroxide being insoluble, it does not allow pH to increase above neutral, whereas hydrogen carbonate being soluble, its excess can make the stomach alkaline and trigger the production of even more acid.
A. Both assertion and reason are correct and reason is the correct explanation for assertion.
B. Both assertion and reason are correct but reason is not the correct explanation for assertion.
C. Assertion is correct but reason is incorrect
D. Both assertion and reason are incorrect

Answer 1

Hint: We know that antacids are effective medicines for gastric problems and heart burns. Many metal hydroxides, metal carbonates and metal bicarbonates are used as antacids. Generally available antacids are magnesium hydroxide, sodium hydrogen carbonate and aluminium hydroxide.

Complete answer:
- We know that antacids are effective medicines for gastric problems and heart burns. Both magnesium hydroxide and sodium hydrogen carbonate are antacids.
- The molecular formula for magnesium hydroxide is ${\text{Mg}}{\left( {{\text{OH}}} \right)_{\text{2}}}$. Magnesium hydroxide is also known as milk of magnesia. Magnesium hydroxide is insoluble in water. Thus, magnesium hydroxide does not change the pH and thus, it does not increase the pH above neutral in the stomach. But magnesium hydroxide neutralizes the acid produced in the stomach.
- The molecular formula for sodium hydrogen carbonate is ${\text{NaHC}}{{\text{O}}_{\text{3}}}$. Sodium hydrogen carbonate is also known as sodium bicarbonate.
- Sodium hydrogen carbonate is soluble in water. Thus, sodium hydrogen carbonate creates an alkaline environment in the stomach. As a result more acid is produced in the stomach. Thus, using sodium hydrogen carbonate as an antacid leads to more problems.
- Thus, the assertion ‘magnesium hydroxide is a better antacid than sodium hydrogen carbonate’ is correct.
- And the reason ‘magnesium hydroxide being insoluble, it does not allow pH to increase above neutral, whereas hydrogen carbonate being soluble, its excess can make the stomach alkaline and trigger the production of even more acid’ is the correct explanation of the reason.

Thus, the correct option is (A) both assertion and reason are correct and reason is the correct explanation for assertion.

Note:
Sodium hydrogen carbonate is a weak base and it is a short-acting antacid. Another disadvantage of sodium hydrogen carbonate is its high sodium content. Sodium hydrogen carbonate can create pH imbalance in the body if used excessively.