Answer: the base in antacid neutralises the extra acid produced in the stomach causing indigestion
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Antacids are mild bases that are used to increase overall ph of the HCl secreted in stomach for proper digestion, it is generally used if there's indigestion due to heavy secretion of HCl, but not to be used in normal way because it can cause increase in ph of gastric acid that causes improper digestion.
That's all ~