---
title: "A student obtains the photoelectron spectrum of a gas-phase sample of an unknown element, \\(\\text{X}\\). The relative area of each peak is proportional to the number of electrons in the corresponding subshell.  Which choice correctly identifies \\(\\text{X}\\) and classifies the peaks at \\(0.50\\ \\text{MJ/mol}\\) and \\(107\\ \\text{MJ/mol}\\)?"
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url: "https://nerd-notes.com/ubq/119494/"
date_modified: "2026-08-19T12:40:45+00:00"
---

# A student obtains the photoelectron spectrum of a gas-phase sample of an unknown element, \(\text{X}\). The relative area of each peak is proportional to the number of electrons in the corresponding subshell.

Which choice correctly identifies \(\text{X}\) and classifies the peaks at \(0.50\ \text{MJ/mol}\) and \(107\ \text{MJ/mol}\)?

A student obtains the photoelectron spectrum of a gas-phase sample of an unknown element, \(\text{X}\). The relative area of each peak is proportional to the number of electrons in the corresponding subshell.

Which choice correctly identifies \(\text{X}\) and classifies the peaks at \(0.50\ \text{MJ/mol}\) and \(107\ \text{MJ/mol}\)?

![Draw a grayscale photoelectron spectrum for a gas-phase sample of element X. Use bare Cartesian axes with no gridlines. Label the horizontal axis Binding energy (MJ/mol) and make binding energy increase from left to right. Include a small zigzag axis break between 10 and 100 to compress the scale. Label the vertical axis Relative peak area with no numerical tick marks. Plot four narrow, solid black, equal-width peaks rising from the baseline. From left to right, center the peaks at 0.50, 3.7, 6.8, and 107, printing each value once below its peak. Their relative areas, in the same order, are exactly 1, 6, 2, and 2; print those four integers once above the corresponding peaks. Make the height of each peak proportional to its area, so the second peak is tallest and the final two have equal heights. No other curves, labels, text, or annotations appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1787143245-wxvtTP.jpg)

- **A.** \(\text{X}\) is \(\text{Ne}\); the \(0.50\ \text{MJ/mol}\) peak represents valence electrons, and the \(107\ \text{MJ/mol}\) peak represents core electrons.
- **B.** \(\text{X}\) is \(\text{Mg}\); the \(0.50\ \text{MJ/mol}\) peak represents valence electrons, and the \(107\ \text{MJ/mol}\) peak represents core electrons.
- **C.** \(\text{X}\) is \(\text{Na}\); the \(0.50\ \text{MJ/mol}\) peak represents core electrons, and the \(107\ \text{MJ/mol}\) peak represents valence electrons.
- **D.** \(\text{X}\) is \(\text{Na}\); the \(0.50\ \text{MJ/mol}\) peak represents valence electrons, and the \(107\ \text{MJ/mol}\) peak represents core electrons.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119494/*