Which of the following is commonly named as caustic soda ?

Options

A. Sodium hydrogen carbonate, dihydrate
B. Sodium carbonate, decahydrate
C. Sodium chloride
D. Sodium hydroxide

Answer

To determine which compound is commonly known as caustic soda, we will analyze the given options step by step.

### Step-by-Step Solution:

1. **Identify the Options**: We have four options to consider:
- Option 1: Sodium hydrogen carbonate dihydrate
- Option 2: Sodium carbonate dihydrate
- Option 3: Sodium chloride
- Option 4: Sodium hydroxide

2. **Analyze Option 1**:
- Sodium hydrogen carbonate dihydrate has the formula NaHCO3·2H2O.
- This compound is commonly known as baking soda, not caustic soda.

3. **Analyze Option 2**:
- Sodium carbonate dihydrate has the formula Na2CO3·10H2O.
- This compound is commonly known as washing soda, not caustic soda.

4. **Analyze Option 3**:
- Sodium chloride has the formula NaCl.
- This compound is commonly known as table salt or common salt, not caustic soda.

5. **Analyze Option 4**:
- Sodium hydroxide has the formula NaOH.
- This compound is commonly known as caustic soda.

6. **Conclusion**:
- Based on the analysis, the compound that is commonly named as caustic soda is **sodium hydroxide (NaOH)**.

### Final Answer:
The correct answer is **Option 4: Sodium hydroxide**.

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