Propanone can be prepared from ethyne by

Options

A. passing a mixture of ethyne and steam over a catalyst, magnesium at `420^(@)C`
B. passing a mixture of ethyne and ethanol over a catalyst zinc chromite
C. boiling ethyne with water and `H_(2)SO_(4)`
D. treating ethyne with lodine and NaOH.

Explanation

To prepare propanone (also known as acetone) from ethyne, we can follow a specific reaction pathway. Here’s the step-by-step solution:

### Step 1: Understand the Reactants and Products
- **Reactant**: Ethyne (C₂H₂)
- **Product**: Propanone (C₃H₆O)

### Step 2: Identify the Reaction
The conversion of ethyne to propanone involves the addition of water (steam) to ethyne in the presence of a catalyst.

### Step 3: Use of Catalyst and Conditions
- The reaction is carried out by passing a mixture of ethyne and steam over a catalyst, typically magnesium oxide (MgO), at a temperature of about 420 degrees Celsius.

### Step 4: Reaction Mechanism
1. **Hydration of Ethyne**: The ethyne reacts with steam in a process called hydration. This reaction adds a water molecule across the triple bond of ethyne.
2. **Formation of Propanone**: The product of this hydration is propan-2-ol (isopropanol), which can then be dehydrated to form propanone.

### Step 5: Final Product
- The final product, propanone, is achieved through the above reaction, confirming that the correct method to prepare propanone from ethyne is indeed by passing ethyne and steam over a catalyst at high temperature.

### Conclusion
Thus, the correct method to prepare propanone from ethyne is:
**Passing a mixture of ethyne and steam over a catalyst (magnesium oxide) at 420 degrees Celsius.**