When acetylene is treated with very dil. HCl in the presence of `HgCl_2`, the product obtained is

Options

A. methyl chloride
B. acetaldehyde
C. vinyl chloride
D. formaldehyde

Explanation

To solve the question, we need to understand the reaction between acetylene (C2H2) and very dilute hydrochloric acid (HCl) in the presence of mercuric chloride (HgCl2). Here’s the step-by-step solution:

### Step 1: Identify the Reactants
The reactants in this reaction are:
- Acetylene (C2H2)
- Very dilute hydrochloric acid (HCl)
- Mercuric chloride (HgCl2) as a catalyst

### Step 2: Understand the Role of HgCl2
HgCl2 acts as a catalyst in this reaction. It facilitates the addition of HCl across the triple bond of acetylene. The presence of HgCl2 allows for a more controlled reaction, leading to the formation of a carbonyl compound rather than an alkane.

### Step 3: Reaction Mechanism
When acetylene reacts with HCl in the presence of HgCl2, the following occurs:
1. The triple bond in acetylene is converted to a double bond as HCl adds across it.
2. The first addition of HCl leads to the formation of vinyl chloride (C2H3Cl).
3. A second addition of HCl occurs, leading to the formation of acetaldehyde (C2H4O).

### Step 4: Identify the Product
The final product of the reaction between acetylene and very dilute HCl in the presence of HgCl2 is acetaldehyde (C2H4O).

### Conclusion
Thus, the product obtained when acetylene is treated with very dilute HCl in the presence of HgCl2 is **acetaldehyde**.

### Answer
The correct answer is **acetaldehyde**.

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