Which of the following species is paramagnetic in nature?

Options

A. Carbonium ion
B. Free radical
C. Singlet Carbene
D. Nitrene

Answer

To determine which of the following species is paramagnetic in nature, we need to identify the presence of unpaired electrons in each species. Paramagnetic species have one or more unpaired electrons, while diamagnetic species have all electrons paired.

### Step-by-Step Solution:

1. **Identify the Species**: The species we need to analyze are:
- Carbonium ion (carbocation)
- Free radical
- Singlet carbene
- Nitrene

2. **Analyze Carbonium Ion**:
- A carbonium ion (e.g., CH3⁺) has three bonds with hydrogen and a positive charge on carbon.
- Carbon has 6 valence electrons. In this case, all electrons can be paired, and there are no unpaired electrons.
- **Conclusion**: Carbonium ion is **not** paramagnetic.

3. **Analyze Free Radical**:
- A free radical (e.g., CH3•) contains one or more unpaired electrons.
- In CH3•, there are three bonds with hydrogen and one unpaired electron.
- **Conclusion**: The free radical has an unpaired electron, making it **paramagnetic**.

4. **Analyze Singlet Carbene**:
- Singlet carbene is a neutral divalent species (e.g., H2C:) with two electrons in the same orbital with opposite spins.
- In this case, all electrons are paired (two in the bond and two in the orbital).
- **Conclusion**: Singlet carbene is **not** paramagnetic.

5. **Analyze Nitrene**:
- Nitrene is a nitrogen analog of carbene and has 6 valence electrons.
- All electrons in nitrene can be paired, meaning there are no unpaired electrons.
- **Conclusion**: Nitrene is **not** paramagnetic.

6. **Final Conclusion**:
- Among the species analyzed, only the **free radical** has unpaired electrons and is therefore paramagnetic.

### Answer:
The species that is paramagnetic in nature is the **free radical**.

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