Which of the following elements [a) Li, b) Na, c) Mg, d) P] contains same number of electrons as that of 's' and 'd' electrons present in Fe+2 ?

Which of the following elements [a) Li, b) Na, c) Mg, d) P] contains same number of electrons as that of 's' and 'd' electrons present in Fe+2 ?

Correct answer is c) Mg

Atomic number of Fe is 26. The electronic configuration of Fe atom is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s². Fe forms Fe⁺² ion on losing the two electrons from 4s orbital.

The electronic configuration of Fe⁺² ion is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶

Total number of ‘d’ electrons (from 3d orbitals) is 6 and number of ‘s’ electrons (taking into account of the electrons from 1s, 2s and 3s orbitals)  = 2+2+2 = 6

Hence, the total number of ‘s’ and ‘d’ electrons in Fe⁺² is = 6+6 =12

Li has atomic number 3 and contains 3 electrons.

Na has atomic number 11 and contains 11 electrons.

Mg has atomic number 12 and contains 12 electrons.

P has atomic number 15 and contains 15 electrons.

Therefore, Mg contains same number of electrons as that of 's' and 'd' electrons present in Fe⁺².