Antacid tablets or medicines are used to neutralize excess stomach acid (hydrochloric acid, HCl) to relieve indigestion and acidity. Antacids are typically bases or basic salts. Let's look at the given options: A) Sodium hydroxide (NaOH): This is a strong base (lye). It is highly corrosive and would cause severe internal burns if ingested. It is not used as an antacid. B) Potassium hydroxide (KOH): Similar to sodium hydroxide, this is also a strong base (caustic potash) and is highly corrosive. It is not used as an antacid. C) Lithium hydroxide (LiOH): A strong base. Not used in antacids. D) Aluminium hydroxide (Al(OH)₃): This is a weak base commonly used in antacid formulations, often combined with magnesium hydroxide (Mg(OH)₂) or calcium carbonate (CaCO₃). Aluminium hydroxide reacts with stomach acid to form aluminium chloride and water: Al(OH)₃(s) + 3HCl(aq) → AlCl₃(aq) + 3H₂O(l). It helps neutralize acid and can also help protect the stomach lining.