The reaction `HC-=CHrarr CHCl_(2)CHO` takes place in

Options

A. `HC-=CHoverset(HOCl)rarr`
B. `HC-=CHunderset("peroxide")overset(HCl)rarr`
C. `HC-=CHoverset(Cl_(2))rarr`
D. `HC-=CHunderset("Oxidizing agent")overset(Cl_(2))rarr`

Answer

To determine the reaction that converts acetylene (HC≡CH) to the compound CHCl₂CHO, we need to analyze the reagents that can facilitate this transformation.

### Step-by-Step Solution:

1. **Identify the Starting Material**:
The starting material is acetylene, represented as HC≡CH. This is a simple alkyne with a triple bond between two carbon atoms.

2. **Identify the Target Compound**:
The target compound is CHCl₂CHO. This compound contains a carbonyl group (C=O) and two chlorine atoms (Cl) attached to one of the carbon atoms.

3. **Consider Possible Reagents**:
To convert acetylene to the desired product, we need to consider reagents that can add chlorine and facilitate the formation of a carbonyl group.

4. **Use of HOCl (Hypochlorous Acid)**:
The reagent HOCl can be used for this reaction. HOCl dissociates into OH⁻ and Cl⁺. The hydroxyl group (OH) acts as a nucleophile, while the chlorine (Cl) acts as an electrophile.

5. **First Reaction Step**:
When acetylene reacts with HOCl, the nucleophile (OH) attacks the electrophile (Cl). This results in the formation of a dichloro compound. The reaction can be visualized as follows:
- HC≡CH + HOCl → CHCl₂C(OH) (dichloro alcohol)

6. **Second Reaction Step**:
The dichloro alcohol can undergo dehydration (loss of water) to form a carbonyl compound. The reaction can be represented as:
- CHCl₂C(OH) → CHCl₂CHO + H₂O

7. **Conclusion**:
The reaction of acetylene with HOCl leads to the formation of CHCl₂CHO through the intermediate dichloro alcohol. Therefore, the correct reagent for this transformation is HOCl.

### Final Answer:
The reaction `HC≡CH → CHCl₂CHO` takes place in the presence of **HOCl (Hypochlorous Acid)**.