---
title: "A student obtains the following schematic photoelectron spectra for \\(3\\) gaseous, isoelectronic samples labeled \\(P\\), \\(Q\\), and \\(R\\). The samples, in unknown order, are \\(\\text{Ne(g)}\\), \\(\\text{Na}^{+}\\text{(g)}\\), and \\(\\text{Mg}^{2+}\\text{(g)}\\). All spectra are plotted on the same relative binding-energy scale.  Which statement correctly identifies the sample whose \\(2p\\) electrons experience the greatest effective nuclear charge and explains the evidence from the spectra?"
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url: "https://nerd-notes.com/ubq/120120/"
date_modified: "2026-08-21T08:42:06+00:00"
---

# A student obtains the following schematic photoelectron spectra for \(3\) gaseous, isoelectronic samples labeled \(P\), \(Q\), and \(R\). The samples, in unknown order, are \(\text{Ne(g)}\), \(\text{Na}^{+}\text{(g)}\), and \(\text{Mg}^{2+}\text{(g)}\). All spectra are plotted on the same relative binding-energy scale.

Which statement correctly identifies the sample whose \(2p\) electrons experience the greatest effective nuclear charge and explains the evidence from the spectra?

A student obtains the following schematic photoelectron spectra for \(3\) gaseous, isoelectronic samples labeled \(P\), \(Q\), and \(R\). The samples, in unknown order, are \(\text{Ne(g)}\), \(\text{Na}^{+}\text{(g)}\), and \(\text{Mg}^{2+}\text{(g)}\). All spectra are plotted on the same relative binding-energy scale.

Which statement correctly identifies the sample whose \(2p\) electrons experience the greatest effective nuclear charge and explains the evidence from the spectra?

![Draw a grayscale photoelectron spectrum with a bare horizontal axis labeled “Relative binding energy” and a vertical axis labeled “Relative number of electrons”; use no gridlines. Values increase from left to right. Plot \(3\) curves from a common baseline. A legend maps \(P\) to a solid line, \(Q\) to a dashed line, and \(R\) to a dotted line. The solid curve has \(3\) narrow peaks centered at horizontal positions \(2\), \(7\), and \(17\), with relative heights \(6\), \(2\), and \(2\), respectively. The dashed curve has peaks at \(3\), \(9\), and \(20\) with the same corresponding heights. The dotted curve has peaks at \(4\), \(11\), and \(23\) with the same corresponding heights. All peaks rise vertically and return sharply to the baseline. No other labels, text, marks, or annotations appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1787301726-qgOerG.jpg)

- **A.** Sample \(R\) is \(\text{Mg}^{2+}\text{(g)}\), because it has fewer occupied principal energy levels than the other samples, resulting in less electron shielding.
- **B.** Sample \(R\) is \(\text{Mg}^{2+}\text{(g)}\), because the species have the same electron configuration, but \(\text{Mg}^{2+}\text{(g)}\) has the greatest nuclear charge and therefore the greatest \(2p\) binding energy.
- **C.** Sample \(P\) is \(\text{Ne(g)}\), because \(\text{Ne}\) has the greatest first ionization energy among the corresponding neutral elements.
- **D.** Sample \(P\) is \(\text{Mg}^{2+}\text{(g)}\), because its greater nuclear charge lowers the energy of a \(2p\) electron, so less energy is required to remove the electron.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/120120/*