Tautomerism is exhibited by :

Options

A.
B.
C.
D.

Explanation

To determine which compounds exhibit tautomerism, we will follow these steps:

### Step 1: Define Tautomerism
Tautomerism is a phenomenon where a single chemical compound can exist in two or more interconvertible structures that differ in the position of atoms, particularly hydrogen atoms.

### Step 2: Identify Alpha Hydrogen
Tautomerism typically occurs in compounds that have alpha hydrogen atoms. An alpha hydrogen is defined as a hydrogen atom attached to a carbon atom that is adjacent to a functional group (like -OH, -CO, etc.).

### Step 3: Analyze Given Compounds
We will look at each compound provided in the question:

1. **Compound A**: Check if it has an alpha hydrogen.
- Identify the functional group (e.g., -OH).
- Find the alpha carbon (the carbon adjacent to the functional group).
- Check if there is a hydrogen atom attached to this alpha carbon.
- If yes, this compound can exhibit tautomerism.

2. **Compound B**: Repeat the process.
- Identify the functional group.
- Locate the alpha carbon.
- Check for alpha hydrogen.
- If no alpha hydrogen is present, it cannot exhibit tautomerism.

3. **Compound C**: Repeat the analysis.
- Identify the functional group.
- Locate the alpha carbon.
- Check for alpha hydrogen.
- If no alpha hydrogen is present, it cannot exhibit tautomerism.

4. **Compound D**: Repeat the analysis.
- Identify the functional group.
- Locate the alpha carbon.
- Check for alpha hydrogen.
- If no alpha hydrogen is present, it cannot exhibit tautomerism.

### Step 4: Conclusion
After analyzing all the compounds, we conclude which compound(s) exhibit tautomerism based on the presence of alpha hydrogen.

### Final Answer
The correct option that exhibits tautomerism is **Option A**.

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