Which of the following is the correct electron configuration for the Co^{2+} ion?

• A. [Ar] 3d^5 4s^2
• B. [Ar] 3d^7
• C. [Ar] 3d^9
• D. [Ar] 3d^6 4s^1

Answer: (B)

Verified step by step guidance

1. Recall that the electron configuration of a neutral cobalt (Co) atom is [Ar] 3d^7 4s^2, where [Ar] represents the argon core electrons.
2. Understand that when forming a Co^{2+} ion, two electrons are removed from the neutral atom. Electrons are removed first from the outermost shell, which is the 4s orbital before the 3d orbitals.
3. Remove the two electrons from the 4s orbital of the neutral cobalt configuration, since 4s electrons are lost before 3d electrons during ionization.
4. After removing two 4s electrons, the electron configuration for Co^{2+} becomes [Ar] 3d^7, as the 3d electrons remain unchanged.
5. Compare this configuration with the given options to identify the correct electron configuration for Co^{2+}.