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:

C and E only

The correct answer is option 3. C and E only.

Antacids are substances that neutralize stomach acid (hydrochloric acid, \(HCl\)) to relieve symptoms of indigestion, heartburn, and acid reflux. Antacids work by directly reacting with \(HCl\), producing neutral salts and water. Their effectiveness depends on how gently they neutralize the acid and whether they avoid causing other unwanted side effects (like gas formation).

Now, let us go through each compound in the question:

A. Sodium carbonate \((Na_2CO_3)\)

Reaction with \(HCl\):

\(Na_2CO_3 + 2HCl \longrightarrow 2NaCl + H_O + CO_2(g)\)

Sodium carbonate (washing soda) is a basic salt and reacts with hydrochloric acid to neutralize it. However, it produces carbon dioxide gas \((CO_2)\) in the process, which can lead to bloating and discomfort in the stomach. 

Due to its strong basicity and the fact that it releases gas, it is not commonly used as an antacid. The gas formation can cause discomfort, which is undesirable in treating acid reflux or heartburn.

Conclusion: Not typically used as an antacid due to these side effects.

B. Trisodium phosphate \((Na_3PO_4)\)

Trisodium phosphate is a strong base, and it has industrial uses, particularly in detergents and cleaning agents. It is not safe for human consumption in significant amounts and is not approved for medical use as an antacid.

Consuming trisodium phosphate can irritate the digestive tract and lead to harmful effects. It is too basic and is not a mild neutralizing agent like other antacids.

Conclusion: Not used as an antacid.

C. Sodium hydrogen carbonate \((NaHCO_3)\) (Baking soda)

Reaction with \(HCl\):

\(NaHCO_3 + HCl \longrightarrow NaCl + H_2O + CO_2(g)\)

Sodium hydrogen carbonate, or baking soda, is a common antacid. It is a weak base that neutralizes stomach acid effectively. When sodium bicarbonate reacts with hydrochloric acid, it produces water, salt (sodium chloride), and carbon dioxide gas.

While it provides quick relief, the production of carbon dioxide can lead to belching and stomach distension. If used in large quantities, it can cause metabolic alkalosis (due to excess bicarbonate in the blood).

Conclusion: Commonly used as an antacid, but its gas-producing reaction limits its use for regular treatment.

D. Aluminium carbonate \((Al_2(CO_3)_3)\)

Reaction with \(HCl\):

\(Al_2(CO_3)_3 + 6HCl \longrightarrow 2AlCl_3 + 3H_2O + 3CO_2(g)\)

Aluminium salts, including aluminium hydroxide and carbonate, are antacids used to neutralize stomach acid. Aluminium carbonate neutralizes \(HCl\), but this reaction also produces carbon dioxide. Despite this, aluminium salts are used in some antacids due to their ability to reduce acid effectively. However, aluminium carbonate is less commonly used compared to aluminium hydroxide

Less frequently used as an antacid than other aluminium-based compounds, and it can lead to constipation and other gastrointestinal side effects.

Conclusion: Can be used as an antacid, but less common in practice.

E. Magnesium hydroxide \((Mg(OH)_2)\)(Milk of Magnesia)

Reaction with \(HCl\):

\(Mg(OH)_2 + 2HCl \longrightarrow MgCl_2 + 2H_2O\)

Magnesium hydroxide is a very common and effective antacid. It neutralizes stomach acid without producing gas and is gentle on the digestive system. It is widely available in over-the-counter formulations, such as Milk of Magnesia, and it acts by neutralizing excess acid to relieve heartburn and indigestion.

If used in large amounts, it can have a laxative effect (because magnesium salts tend to draw water into the intestines).

Conclusion: Commonly used as an antacid, and it is one of the safest and most effective compounds for this purpose.

Thus, the correct answer is option 3: C and E only.