Which one of the following acts as an antichlor ?

Options

A. `MnO_(2)`
B. `Na_(2)S_(2)O_(3)`
C. `K_(2)Cr_(2)O_(7)`
D. `Na_(2)SO_(4)`

Answer

To determine which of the given options acts as an antichlor, we need to understand what an antichlor is and its function.

### Step-by-Step Solution:

1. **Definition of Antichlor**:
- An antichlor is a substance that is used to neutralize or decompose residual chlorine or hydrochloric acid (HCl) after chlorine-based bleaching processes. This is important to prevent any ongoing reactions that could damage the bleached material.

2. **Identifying the Options**:
- We have the following options to consider:
- A) Mn (Manganese)
- B) Na2S2O3 (Sodium thiosulfate)
- C) K2Cr2O7 (Potassium dichromate)
- D) Na2SO4 (Sodium sulfate)

3. **Evaluating Each Option**:
- **A) Mn (Manganese)**: This is not known to act as an antichlor. Incorrect.
- **B) Na2S2O3 (Sodium thiosulfate)**: This compound is well-known for its ability to neutralize chlorine and is commonly used as an antichlor. Correct.
- **C) K2Cr2O7 (Potassium dichromate)**: This is a strong oxidizing agent and does not function as an antichlor. Incorrect.
- **D) Na2SO4 (Sodium sulfate)**: This compound does not have the properties of an antichlor. Incorrect.

4. **Conclusion**:
- The only substance among the options that acts as an antichlor is **B) Na2S2O3 (Sodium thiosulfate)**.

### Final Answer:
- The correct answer is **B) Na2S2O3 (Sodium thiosulfate)**.