In the ground-state electron configuration of Fe^{3+}, how many unpaired electrons are present?

• A. 2
• B. 0
• C. 5
• D. 3

Answer: (C)

Verified step by step guidance

1. Identify the atomic number of iron (Fe), which is 26, meaning a neutral Fe atom has 26 electrons.
2. Determine the electron configuration of the neutral Fe atom in its ground state. The configuration is \$1s^2 2s^2 2p^6 3s^2 3p^6 3d^6 4s^2$.
3. Since Fe^{3+} means the iron ion has lost 3 electrons, remove electrons first from the 4s orbital and then from the 3d orbital, because 4s electrons are lost before 3d electrons.
4. After removing 3 electrons, write the electron configuration for Fe^{3+}, which will be \([Ar] 3d^5\).
5. Determine the number of unpaired electrons in the \$3d^5$ configuration by applying Hund's rule, which states that electrons fill degenerate orbitals singly before pairing up, resulting in 5 unpaired electrons.