How many electrons are present in the 3d subshell of the Co³⁺ ion (Co, Z = 27)?
Correct answer C. 6
Explanation
Cobalt is [Ar]3d⁷4s². Removing the two 4s electrons and one 3d electron gives Co³⁺ = [Ar]3d⁶, so there are 6 electrons in the 3d subshell.
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