To solve the question regarding the number of 'd' electrons in \( \text{Fe}^{2+} \) and how it compares to other elements, we can follow these steps:
### Step 1: Determine the electron configuration of neutral iron (Fe).
- The atomic number of iron (Fe) is 26.
- The electron configuration of neutral iron is:
\[
\text{Fe}: 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^6
\]
### Step 2: Determine the electron configuration of \( \text{Fe}^{2+} \).
- To find the electron configuration of \( \text{Fe}^{2+} \), we need to remove two electrons from the neutral iron configuration.
- Electrons are removed first from the 4s subshell before the 3d subshell:
\[
\text{Fe}^{2+}: 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 3d^6 \, \text{(remove 2 from 4s)} \Rightarrow 3d^6
\]
- Therefore, the electron configuration of \( \text{Fe}^{2+} \) is:
\[
1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 3d^6
\]
### Step 3: Count the number of 'd' electrons in \( \text{Fe}^{2+} \).
- From the configuration \( 3d^6 \), we can see that there are 6 'd' electrons in \( \text{Fe}^{2+} \).
### Step 4: Compare with the options provided.
1. **S electrons in Magnesium (Mg)**:
- Magnesium has an atomic number of 12. Its electron configuration is:
\[
\text{Mg}: 1s^2 \, 2s^2 \, 2p^6 \, 3s^2
\]
- The number of 's' electrons in Mg is 2 (from the 3s subshell).
2. **P electrons in Neon (Ne)**:
- Neon has an atomic number of 10. Its electron configuration is:
\[
\text{Ne}: 1s^2 \, 2s^2 \, 2p^6
\]
- The number of 'p' electrons in Ne is 6 (from the 2p subshell).
3. **P electrons in Chlorine (Cl)**:
- Chlorine has an atomic number of 17. Its electron configuration is:
\[
\text{Cl}: 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^5
\]
- The number of 'p' electrons in Cl is 5 (from the 3p subshell).
4. **D electrons in Fe**:
- As calculated, the number of 'd' electrons in \( \text{Fe}^{2+} \) is 6.
### Conclusion:
- The number of 'd' electrons in \( \text{Fe}^{2+} \) is 6, which is not equal to the number of 's' electrons in Mg (2), the number of 'p' electrons in Ne (6), or the number of 'p' electrons in Cl (5).
- Therefore, the correct answer is that the number of 'd' electrons in \( \text{Fe}^{2+} \) is not equal to the number of 's' electrons in Mg.
