Which of the following is/ are antacids?
A. Sodium carbonate
B. Trisodium phosphate
C. Sodium hydrogen carbonate
D. Aluminium carbonate
E. Magnesium hydroxide
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → C and E only
Antacids neutralise the excess hydrochloric acid in the stomach. They must be mild bases that do not harm the body. The usual antacids are sodium hydrogencarbonate and a mixture of aluminium and magnesium hydroxides; the insoluble metal hydroxides are better because they do not raise the pH above neutral.
(A) Sodium carbonate — Not an antacid. \( \ce{Na2CO3} \) (washing soda) is too strongly alkaline and corrosive to be swallowed.
(B) Trisodium phosphate — Not an antacid. \( \ce{Na3PO4} \) is a strongly alkaline cleaning agent, not a medicine.
(C) Sodium hydrogen carbonate — Antacid. It neutralises the excess acid:
\( \displaystyle \ce{NaHCO3 + HCl -> NaCl + H2O + CO2} \)
(D) Aluminium carbonate — Not an antacid. The aluminium antacid is aluminium hydroxide, \( \ce{Al(OH)3} \), not the carbonate.
(E) Magnesium hydroxide — Antacid. Being insoluble, it does not make the stomach alkaline:
\( \displaystyle \ce{Mg(OH)2 + 2HCl -> MgCl2 + 2H2O} \)
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Antacids – “Over production of acid in the stomach causes irritation and pain. In severe cases, ulcers are developed in the stomach. Until 1970, only treatment for acidity was administration of antacids, such as sodium hydrogencarbonate or a mixture of aluminium and magnesium hydroxide. However, excessive hydrogencarbonate can make the stomach alkaline and trigger the production of even more acid. Metal hydroxides are better alternatives because of being insoluble, these do not increase the pH above neutrality.”