Which of the following is an antacid?

Options

A. Sodium carbonate
B. Magnesium hydroxide
C. Sodium chloride
D. Alum

Answer

To determine which of the following compounds is an antacid, we will analyze each option provided: Sodium Carbonate, Magnesium Hydroxide, and Sodium Chloride.

### Step-by-Step Solution:

1. **Understanding Antacids**:
- Antacids are substances that neutralize stomach acidity. They are typically basic in nature and help in increasing the pH level in the stomach, providing relief from conditions like indigestion and heartburn.

2. **Analyzing Sodium Carbonate (Na2CO3)**:
- Sodium Carbonate is a white, water-soluble compound commonly known as washing soda. While it is basic, it is not primarily used as an antacid. Its main applications are in cleaning and as a pH regulator in various industrial processes.

3. **Analyzing Magnesium Hydroxide (Mg(OH)2)**:
- Magnesium Hydroxide is a compound that is known for its antacid properties. It is derived from the mineral brucite and is widely used to relieve indigestion and heartburn. It works by neutralizing stomach acid and is also used as a laxative.

4. **Analyzing Sodium Chloride (NaCl)**:
- Sodium Chloride, commonly known as table salt, is composed of sodium and chloride ions. It does not have antacid properties and is primarily used to regulate fluid balance in the body and as a seasoning in food.

5. **Conclusion**:
- Among the three options, **Magnesium Hydroxide** is the only compound that functions as an antacid.

### Final Answer:
**Magnesium Hydroxide** is the antacid.