Ethyne adds a molecule of methyl alcohol in the presence of alkali to give

Options

A. Acetone
B. Methyl vinyl ether
C. Acetaldehyde
D. Acetic acid

Explanation

To solve the question "Ethyne adds a molecule of methyl alcohol in the presence of alkali to give?", we will follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**:
- The reactants are Ethyne (C2H2) and methyl alcohol (methanol, CH3OH).

2. **Understand the Reaction Conditions**:
- The reaction occurs in the presence of an alkali, which can be represented by a base like NaOH.

3. **Draw the Structure of Ethyne**:
- Ethyne has a triple bond between the two carbon atoms: H-C≡C-H.

4. **Identify the Role of the Base (Alkali)**:
- The base will abstract a proton (H+) from the ethyne. Since ethyne has acidic hydrogen due to its sp hybridization, the hydrogen is more likely to be removed.

5. **Proton Abstraction**:
- The base (OH-) will abstract one proton from ethyne, resulting in the formation of an ethynyl anion (HC≡C^-).

6. **Formation of Alkoxide Ion**:
- The base will also interact with methanol (CH3OH) to form an alkoxide ion (CH3O^-). The proton from methanol is abstracted by the base.

7. **Nucleophilic Attack**:
- The alkoxide ion (CH3O^-) will attack the ethynyl anion (HC≡C^-). This forms a new carbon-oxygen bond.

8. **Formation of the Product**:
- The product formed will be methyl vinyl ether (H2C=CH-O-CH3). The double bond forms between the two carbon atoms, and the oxygen from the methanol is now bonded to one of the carbon atoms.

9. **Final Structure**:
- The final structure can be represented as H2C=CH-O-CH3, which is methyl vinyl ether.

### Conclusion:
Thus, the product of the reaction between ethyne and methyl alcohol in the presence of alkali is **methyl vinyl ether**.

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