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 resonance and the presence of electron-donating or electron-withdrawing groups.

### Step-by-Step Solution:

1. **Identify the Radicals**:
- List the radicals provided in the question. For example, let's assume the options are:
a) Benzyl radical (C6H5-CH2•)
b) Allyl radical (C3H5•)
c) Tertiary butyl radical (C(CH3)3•)
d) Methyl radical (CH3•)

2. **Analyze Resonance Structures**:
- **Benzyl Radical**: This radical can delocalize the unpaired electron over the aromatic ring through resonance. It has multiple resonance structures which stabilize it.
- **Allyl Radical**: This radical also has resonance stabilization as the unpaired electron can be shared between the two carbon atoms adjacent to the radical center.
- **Tertiary Butyl Radical**: This radical is stabilized by hyperconjugation from the three methyl groups surrounding the central carbon atom, providing significant stability.
- **Methyl Radical**: This radical has no resonance stabilization and is only stabilized by hyperconjugation from the hydrogen atoms, which is minimal.

3. **Compare Stability**:
- The stability of radicals generally follows this order:
- Tertiary > Secondary > Primary > Methyl.
- Benzyl and allyl radicals are stabilized by resonance, making them more stable than the methyl radical.
- The tertiary butyl radical is the most stable due to hyperconjugation.

4. **Conclusion**:
- Among the radicals analyzed, the methyl radical (CH3•) is the least stable due to the lack of resonance and minimal hyperconjugation.

### Final Answer:
The least stable radical among the given options is the **Methyl radical (CH3•)**.