If Hund's rule is not obeyed by some element given below then which atom has maximum magnetic moment

Options

A. Fe
B. Cu
C. Cr
D. Mn

Explanation

To determine which atom has the maximum magnetic moment when Hund's rule is not obeyed, we will analyze the electronic configurations of the given elements: Iron (Fe), Copper (Cu), Chromium (Cr), and Manganese (Mn).

### Step-by-Step Solution:

1. **Understanding Hund's Rule**:
- Hund's rule states that electrons will fill degenerate orbitals (orbitals of the same energy) singly before pairing up. This means that the maximum number of unpaired electrons will be present when Hund's rule is followed.

2. **Electronic Configurations**:
- **Iron (Fe)**: The electronic configuration is \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^6\).
- **Copper (Cu)**: The electronic configuration is \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^{10}\).
- **Chromium (Cr)**: The electronic configuration is \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^5\).
- **Manganese (Mn)**: The electronic configuration is \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^5\).

3. **Applying Hund's Rule**:
- **Iron**: If Hund's rule is not followed, the distribution of electrons would be \(3d^6\) as \(↑↑↑↑↑↑\) (all paired), resulting in **0 unpaired electrons** (diamagnetic).
- **Copper**: If Hund's rule is not followed, the distribution would be \(4s^2 3d^{10}\) as \(↑↑\) (all paired), resulting in **0 unpaired electrons** (diamagnetic).
- **Chromium**: If Hund's rule is not followed, the distribution would be \(4s^2 3d^5\) as \(↑↑↑↑↑\) (all paired), resulting in **0 unpaired electrons** (diamagnetic).
- **Manganese**: If Hund's rule is not followed, the distribution would be \(4s^2 3d^5\) as \(↑↑↑↑↑\) (all paired), resulting in **0 unpaired electrons** (diamagnetic).

4. **Identifying Magnetic Moments**:
- The magnetic moment is determined by the number of unpaired electrons. The more unpaired electrons, the higher the magnetic moment.
- From our analysis, both Copper and Iron become diamagnetic with no unpaired electrons when Hund's rule is not followed.

5. **Conclusion**:
- Since all the elements analyzed become diamagnetic (0 unpaired electrons) when Hund's rule is not obeyed, they do not exhibit a magnetic moment. However, if we consider the original configurations where Hund's rule is followed, Copper and Manganese would have the maximum magnetic moment due to their unpaired electrons.

### Final Answer:
The atom with the maximum magnetic moment when Hund's rule is not obeyed is **Copper (Cu)** and **Manganese (Mn)**, as they both have the same number of unpaired electrons when Hund's rule is followed.