The number of $\mathrm{d}$-electrons in ${\mathrm{Fe}}^{2+} (\mathrm{Z}=26)$ is not equal to the number of electrons in which one of the following?

• A

  $\mathrm{s}$-electrons in $\mathrm{Mg} \left(\mathrm{Z}=12\right)$
• Correct answer
  B

  $\mathrm{p}$-electrons in $\mathrm{Cl} \left(\mathrm{Z}=17\right)$
• C

  $\mathrm{d}$-electrons in $\mathrm{Fe} \left(\mathrm{Z}=26\right)$
• D

  $\mathrm{p}$-electrons in $\mathrm{Ne} \left(\mathrm{Z}=10\right)$

Hence, the correct answer is option: 'B'.