Least stable radical among the following is :

Options

A.
B.
C.
D.

Answer

To determine the least stable radical among the given options, we need to analyze the stability of each radical based on the number of resonance structures (conjugating structures) they can form. The more resonance structures a radical can form, the more stable it is.

### Step-by-Step Solution:

1. **Identify the Radicals**:
- Look at the provided options and identify the radicals present in each structure.

2. **Analyze Each Option**:
- **Option A**: Contains a six-membered ring with two double bonds. The radical can form multiple resonance structures due to the presence of the double bonds.
- **Option B**: Similar to option A, it also has a structure that allows for multiple resonance forms due to the presence of double bonds.
- **Option C**: Contains a radical adjacent to a double bond in a six-membered ring. This structure can only form one resonance structure because after the initial radical formation, further conjugation is limited.
- **Option D**: Like options A and B, it has two double bonds that allow for resonance stabilization.

3. **Count the Resonance Structures**:
- **Option A**: Can form at least two resonance structures.
- **Option B**: Can also form at least two resonance structures.
- **Option C**: Can only form one resonance structure.
- **Option D**: Can form at least two resonance structures.

4. **Determine Stability**:
- The stability of radicals increases with the number of resonance structures. Therefore, the radical in **Option C**, which can only form one resonance structure, is the least stable.

5. **Conclusion**:
- The least stable radical among the options provided is **Option C**.

### Final Answer:
**Option C is the least stable radical.**