Which of the following can exhibit tautomerism:

Options

A.
B.
C.
D.

Answer

To determine which of the given options can exhibit tautomerism, we need to analyze the structures provided in each option. Tautomerism typically involves the migration of a hydrogen atom and a shift of a double bond, often resulting in a keto-enol tautomeric relationship.

### Step-by-Step Solution:

1. **Identify the Structures**:
- Write down the structures for each option provided in the question.

2. **Analyze Each Structure for Tautomerism**:
- **Option A**:
- Identify the alpha carbon and the presence of a carbonyl group (C=O).
- Check if there are any alpha hydrogens that can migrate to the carbonyl carbon.
- In this case, the presence of a bicyclic structure creates strain when attempting to form an enol, making it unstable. Therefore, tautomerism is not favorable.

- **Option B**:
- Similar analysis as in Option A.
- Identify the alpha hydrogens and the carbonyl group.
- Here, the structure allows for the migration of an alpha hydrogen to the carbonyl carbon without significant strain, making it more stable and capable of tautomerism.

- **Option C**:
- Again, identify the alpha hydrogens and carbonyl group.
- The presence of conjugated double bonds in a cyclic structure prevents the formation of an enol form. Thus, tautomerism is not possible.

- **Option D**:
- Analyze the structure for alpha hydrogens and carbonyl group.
- Similar to Option C, the cyclic structure with double bonds does not allow for the formation of an enol form, so tautomerism is not feasible.

3. **Conclusion**:
- After analyzing all options, only **Option B** allows for the formation of an enol form due to the absence of significant strain and the presence of alpha hydrogens that can migrate to the carbonyl carbon.

### Final Answer:
The only structure that can exhibit tautomerism is **Option B**.