---
title: "An isolated neutral iron atom ( \\(\\text{Fe}\\), \\(Z = 26\\)) in the gas phase has the ground-state electron configuration \\([\\text{Ar}]\\, 4s^2 3d^6\\). The atom undergoes three successive ionizations to produce \\(\\text{Fe}^+\\text{(g)}\\), \\(\\text{Fe}^{2+}\\text{(g)}\\), and \\(\\text{Fe}^{3+}\\text{(g)}\\). Which of the following correctly predicts the ground-state electron configurations of \\(\\text{Fe}^{2+}\\) and \\(\\text{Fe}^{3+}\\), and identifies the subshell from which the third electron is removed?"
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url: "https://nerd-notes.com/ubq/123509/"
date_modified: "2026-09-28T11:59:59+00:00"
---

# An isolated neutral iron atom (
\(\text{Fe}\), \(Z = 26\)) in the gas phase has the ground-state electron configuration \([\text{Ar}]\, 4s^2 3d^6\). The atom undergoes three successive ionizations to produce \(\text{Fe}^+\text{(g)}\), \(\text{Fe}^{2+}\text{(g)}\), and \(\text{Fe}^{3+}\text{(g)}\). Which of the following correctly predicts the ground-state electron configurations of \(\text{Fe}^{2+}\) and \(\text{Fe}^{3+}\), and identifies the subshell from which the third electron is removed?

An isolated neutral iron atom (
\(\text{Fe}\), \(Z = 26\)) in the gas phase has the ground-state electron configuration \([\text{Ar}]\, 4s^2 3d^6\). The atom undergoes three successive ionizations to produce \(\text{Fe}^+\text{(g)}\), \(\text{Fe}^{2+}\text{(g)}\), and \(\text{Fe}^{3+}\text{(g)}\). Which of the following correctly predicts the ground-state electron configurations of \(\text{Fe}^{2+}\) and \(\text{Fe}^{3+}\), and identifies the subshell from which the third electron is removed?

- **A.** \(\text{Fe}^{2+}\) is \([\text{Ar}]\, 4s^2 3d^4\), \(\text{Fe}^{3+}\) is \([\text{Ar}]\, 4s^1 3d^4\), and the third electron is removed from the \(4s\) subshell.
- **B.** \(\text{Fe}^{2+}\) is \([\text{Ar}]\, 3d^6\), \(\text{Fe}^{3+}\) is \([\text{Ar}]\, 3d^5\), and the third electron is removed from the \(3d\) subshell.
- **C.** \(\text{Fe}^{2+}\) is \([\text{Ar}]\, 4s^1 3d^5\), \(\text{Fe}^{3+}\) is \([\text{Ar}]\, 3d^5\), and the third electron is removed from the \(4s\) subshell.
- **D.** \(\text{Fe}^{2+}\) is \([\text{Ar}]\, 4s^2 3d^4\), \(\text{Fe}^{3+}\) is \([\text{Ar}]\, 3d^5\), and the third electron is removed from the \(4s\) subshell.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123509/*