Which of the following molecule is not paramagnetic :

Options

A. `Cu^(++)`
B. `Fe^(2+)`
C. `CI^(-)`
D. None of the above

Answer

To determine which of the given molecules is not paramagnetic, we need to analyze the electronic configurations of each species and identify the presence of unpaired electrons. A molecule is paramagnetic if it has unpaired electrons, while it is diamagnetic if all its electrons are paired.

### Step-by-Step Solution:

1. **Identify the Given Molecules:**
- Cu²⁺ (Copper ion)
- Fe²⁺ (Iron ion)
- Cl⁻ (Chloride ion)
- None of the above

2. **Analyze Cu²⁺:**
- The atomic number of copper (Cu) is 29.
- The electronic configuration of Cu is:
\[ [Ar] 3d^{10} 4s^1 \]
- For Cu²⁺, we remove two electrons. The first electron is removed from the 4s orbital, and the second from the 3d orbital:
\[ Cu^{2+} \rightarrow [Ar] 3d^9 \]
- In the 3d subshell, there are 9 electrons, which means there is 1 unpaired electron. Therefore, Cu²⁺ is **paramagnetic**.

3. **Analyze Fe²⁺:**
- The atomic number of iron (Fe) is 26.
- The electronic configuration of Fe is:
\[ [Ar] 4s^2 3d^6 \]
- For Fe²⁺, we remove two electrons from the 4s orbital:
\[ Fe^{2+} \rightarrow [Ar] 3d^6 \]
- In the 3d subshell, there are 6 electrons. The distribution of these electrons can be represented as:
\[ 3d: \uparrow \downarrow \uparrow \uparrow \uparrow \uparrow \]
- There are 4 unpaired electrons in the 3d subshell. Therefore, Fe²⁺ is **paramagnetic**.

4. **Analyze Cl⁻:**
- The atomic number of chlorine (Cl) is 17.
- The electronic configuration of Cl is:
\[ [Ne] 3s^2 3p^5 \]
- For Cl⁻, we add one electron:
\[ Cl^{-} \rightarrow [Ne] 3s^2 3p^6 \]
- The configuration for Cl⁻ is:
\[ 1s^2 2s^2 2p^6 3s^2 3p^6 \]
- All orbitals are filled, meaning there are no unpaired electrons. Therefore, Cl⁻ is **not paramagnetic** (it is diamagnetic).

5. **Conclusion:**
- Among the given molecules, Cl⁻ is the only one that is not paramagnetic. Therefore, the correct answer is:
- **Cl⁻ is not paramagnetic.**

### Final Answer:
**Cl⁻ is the molecule that is not paramagnetic.**