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The number of d-electrons in Fe²⁺ (Z = 26) is not equal to the number of electrons in which one of the following?

1. p-electrons in Cl (Z = 17)
2. d-electrons in Fe (Z = 26)
3. p-electrons in Ne (Z = 10)
4. s-electrons in Mg (Z = 12)

Correct answer: s-electrons in Mg (Z = 12)

Solution

Fe²⁺ has 6 d-electrons, while Mg has 2 s-electrons.

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