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Question:

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

d - electrons in Fe (Z=26)

s - electrons in Mg (Z=12)

p - electrons in Ne (Z=10)

p - electrons in Cl (Z=17)

Solution:

The electronic configuration of Fe (Z=26) is [Ar] 3d⁶ 4s².
Fe²⁺ is formed by the loss of two electrons from the 4s orbital. Thus, the electronic configuration of Fe²⁺ is [Ar] 3d⁶.
Therefore, the number of d-electrons in Fe²⁺ is 6.
Now let's check the options:

  1. d-electrons in Fe (Z=26): Fe has 6 d-electrons.
  2. s-electrons in Mg (Z=12): The electronic configuration of Mg is [Ne] 3s². Mg has 2 s-electrons.
  3. p-electrons in Ne (Z=10): The electronic configuration of Ne is 1s² 2s² 2p⁶. Ne has 6 p-electrons.
  4. p-electrons in Cl (Z=17): The electronic configuration of Cl is [Ne] 3s² 3p⁵. Cl has 5 p-electrons.
    The number of d-electrons in Fe²⁺ (6) is not equal to the number of p-electrons in Cl (5).