Which of the following is a common antacid ?

Options

A. `NaOH`
B. `Ca(OH)_2`
C. `Mg(OH)_2`
D. `KOH`

Explanation

To determine which of the given options is a common antacid, we need to analyze each option based on its properties and uses.

### Step-by-Step Solution:

1. **Understanding Antacids**:
- Antacids are substances that help neutralize stomach acidity. They are typically basic in nature, which means they can counteract the acidity in the stomach.

2. **Analyzing the Options**:
- The options provided are:
- a) NaOH (Sodium Hydroxide)
- b) Ca(OH)₂ (Calcium Hydroxide)
- c) Mg(OH)₂ (Magnesium Hydroxide)
- d) KOH (Potassium Hydroxide)

3. **Evaluating NaOH**:
- Sodium Hydroxide (NaOH) is a strong base. It is highly corrosive and not suitable for medicinal use, especially as an antacid. Therefore, NaOH is not a common antacid.

4. **Evaluating Ca(OH)₂**:
- Calcium Hydroxide (Ca(OH)₂), also known as slaked lime, is slightly basic but primarily used in construction (mortar, plaster, cement) and not in medicine. Thus, it is not considered a common antacid.

5. **Evaluating Mg(OH)₂**:
- Magnesium Hydroxide (Mg(OH)₂) is commonly used as an antacid. It is effective in neutralizing stomach acid and is often found in over-the-counter antacid medications. Therefore, Mg(OH)₂ is a common antacid.

6. **Evaluating KOH**:
- Potassium Hydroxide (KOH) is another strong base that is corrosive and not suitable for use as an antacid. Similar to NaOH, it can cause harm if ingested.

7. **Conclusion**:
- Among the options provided, the only common antacid is **c) Mg(OH)₂ (Magnesium Hydroxide)**.

### Final Answer:
The correct answer is **c) Mg(OH)₂ (Magnesium Hydroxide)**.