Why cimetidine and ranitidine are are better antacids than `NaHCO_3 or Mg(OH)_2 or Al(OH)_3` ?

Explanation

### Step-by-Step Solution:

1. **Understanding Antacids**:
- Antacids are substances that neutralize stomach acidity. They work by counteracting the excess hydrochloric acid (HCl) in the stomach, which can cause discomfort and ulcers.

2. **Mechanism of Action**:
- Cimetidine and ranitidine are classified as H2 receptor antagonists. They work by blocking the H2 receptors in the stomach lining, which are responsible for stimulating the secretion of gastric acid. This results in a decrease in the production of H+ ions, effectively reducing acidity at the source.

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