Which of the following cannot be used for the preaparation of iodofrom ?

Options

A. Acetone
B. Methanol
C. Ethanol
D. Acetealdeyde

Explanation

To determine which of the given compounds cannot be used for the preparation of iodoform (CHI3), we need to understand the conditions under which iodoform can be formed. The iodoform test is positive for compounds that contain a methyl ketone group (RCOCH3) or certain types of alcohols that can be oxidized to form a methyl ketone.

### Step-by-Step Solution:

1. **Identify the Required Functional Groups**:
- Iodoform can be formed from compounds that have a methyl ketone group (RCOCH3) or alcohols that can be oxidized to form such a group.

2. **Analyze Each Compound**:
- **Compound A: Acetone (CH3COCH3)**:
- Acetone is a ketone with a methyl group attached to the carbonyl carbon. It has the structure CH3COCH3, which fits the criteria for the iodoform test. Therefore, acetone can be used to prepare iodoform.

- **Compound B: Methanol (CH3OH)**:
- Methanol is a simple alcohol with the structure CH3OH. It does not have a methyl ketone group and cannot be oxidized to form one. Therefore, methanol cannot be used to prepare iodoform.

- **Compound C: Ethanol (C2H5OH)**:
- Ethanol is a two-carbon alcohol (C2H5OH). It can be oxidized to acetaldehyde (CH3CHO), which has a methyl group adjacent to the carbonyl group. Thus, ethanol can also give a positive iodoform test.

- **Compound D: Acetaldehyde (CH3CHO)**:
- Acetaldehyde is a two-carbon aldehyde with the structure CH3CHO. It contains a methyl group adjacent to the carbonyl group, allowing it to give a positive iodoform test as well.

3. **Conclusion**:
- Among the compounds analyzed, methanol (Compound B) is the only one that cannot be used to prepare iodoform. Therefore, the answer is methanol.

### Final Answer:
**Methanol (Option B) cannot be used for the preparation of iodoform.**