---
title: "A pure sample of an unknown gaseous element is analyzed using mass spectrometry. During the ionization process, some neutral diatomic molecules undergo fragmentation into monatomic ions, while other molecules remain intact and form molecular ions with a \\(+1\\) charge. The resulting mass spectrum contains two distinct clusters of peaks, as shown in the graph.  Based on the mass spectrum, which of the following is the identity of the element?"
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url: "https://nerd-notes.com/ubq/123506/"
date_modified: "2026-09-28T11:59:59+00:00"
---

# A pure sample of an unknown gaseous element is analyzed using mass spectrometry. During the ionization process, some neutral diatomic molecules undergo fragmentation into monatomic ions, while other molecules remain intact and form molecular ions with a \(+1\) charge. The resulting mass spectrum contains two distinct clusters of peaks, as shown in the graph.

Based on the mass spectrum, which of the following is the identity of the element?

A pure sample of an unknown gaseous element is analyzed using mass spectrometry. During the ionization process, some neutral diatomic molecules undergo fragmentation into monatomic ions, while other molecules remain intact and form molecular ions with a \(+1\) charge. The resulting mass spectrum contains two distinct clusters of peaks, as shown in the graph.

Based on the mass spectrum, which of the following is the identity of the element?

![A grayscale mass spectrum graph with no gridlines. The horizontal axis is labeled Mass-to-charge ratio (m/z) and ranges from 0 to 180, with major tick marks labeled at 0, 40, 80, 120, 160, and 180. The vertical axis is labeled Relative Abundance (%) and ranges from 0 to 100, with tick marks labeled at 0, 50, and 100. There are five vertical black signal lines representing peaks. In the lower-mass cluster, two lines appear: a line at m/z = 79 with a height of 50%, and a line at m/z = 81 with a height of 50%. In the higher-mass cluster, three lines appear: a line at m/z = 158 with a height of 25%, a line at m/z = 160 with a height of 50%, and a line at m/z = 162 with a height of 25%. No other peaks, gridlines, labels, text, or annotations appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1790596798-LfZuiH.jpg)

- **A.** \(\text{Cl}\)
- **B.** \(\text{Ar}\)
- **C.** \(\text{Se}\)
- **D.** \(\text{Br}\)

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123506/*