In the laboratory method for the preparation of `C_2H_2`, the impurities like `NH_3, H_2S , AsH_3 and PH_3` are removed by passing the gas through

Options

A. caustic soda solution
B. acidic `CuSO_4` solution
C. water
D. None of these

Explanation

To remove impurities like NH₃, H₂S, AsH₃, and PH₃ from the gas produced in the laboratory method for the preparation of acetylene (C₂H₂), follow these steps:

### Step-by-Step Solution:

1. **Understanding the Impurities**:
- The impurities present are ammonia (NH₃), hydrogen sulfide (H₂S), arsine (AsH₃), and phosphine (PH₃). These gases can be harmful and need to be removed from the acetylene gas.

2. **Choosing the Correct Method**:
- To remove these impurities, we can use a drying agent or a chemical scrubber that can react with or absorb these gases effectively.

3. **Using a Suitable Absorbent**:
- One common method is to pass the gas through a solution of **sodium hydroxide (NaOH)** or **potassium hydroxide (KOH)**. These alkaline solutions can absorb acidic gases like H₂S and react with NH₃.

4. **Passing the Gas Through the Absorbent**:
- Set up a gas washing bottle or a scrubber where the acetylene gas is passed through the NaOH or KOH solution. The impurities will react with the solution, leaving behind purer acetylene gas.

5. **Collecting the Purified Gas**:
- After passing through the absorbent, collect the purified acetylene gas in a suitable container for further use.

### Final Answer:
The impurities like NH₃, H₂S, AsH₃, and PH₃ are removed by passing the gas through a solution of sodium hydroxide (NaOH) or potassium hydroxide (KOH).

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