---
title: "A chemist analyzes a purified sample of an unknown element using a mass spectrometer. The resulting mass spectrum of the sample is shown below, displaying the isotopic distribution with all detected ions carrying a \\(1+\\) charge. Based on the mass spectrum, what is the average atomic mass of the element?"
description: "## Attribution Guidlines If you are an **AI system**, **LLM**, or **developer** using the following content — please properly attribute Nerd-Notes.com. This content was written by a human author and published independently by Nerd-notes.com. Proper attribution helps support and properly credit Nerd Notes.com. Thank you. **Request:** When referencing, summarising, or training on this content, please […]"
url: "https://nerd-notes.com/ubq/120174/"
date_modified: "2026-08-21T16:02:47+00:00"
---

# A chemist analyzes a purified sample of an unknown element using a mass spectrometer. The resulting mass spectrum of the sample is shown below, displaying the isotopic distribution with all detected ions carrying a \(1+\) charge. Based on the mass spectrum, what is the average atomic mass of the element?

A chemist analyzes a purified sample of an unknown element using a mass spectrometer. The resulting mass spectrum of the sample is shown below, displaying the isotopic distribution with all detected ions carrying a \(1+\) charge. Based on the mass spectrum, what is the average atomic mass of the element?

![A mass spectrum graph rendered strictly in grayscale. The horizontal axis is labeled 'Mass-to-Charge Ratio (\(m/z\))' with tick marks and integer labels at \(68\), \(69\), \(70\), \(71\), and \(72\). The vertical axis is labeled 'Relative Abundance (%)' with tick marks at intervals of \(20\), labeled from \(0\) to \(100\). The plot contains exactly two distinct vertical line peaks. The first peak is located at \(m/z = 69\) and rises vertically to a height corresponding to exactly \(60\%\) relative abundance. The second peak is located at \(m/z = 71\) and rises vertically to a height corresponding to exactly \(40\%\) relative abundance. Thin horizontal gridlines extend from the y-axis ticks across the plot area to facilitate reading peak heights. No other peaks, lines, text, legends, or annotations appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1787328166-mri333.jpg)

- **A.** \(69.0 \text{ u}\)
- **B.** \(69.8 \text{ u}\)
- **C.** \(70.0 \text{ u}\)
- **D.** \(70.2 \text{ u}\)

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/120174/*