---
title: "The complete photoelectron spectrum of a neutral atom of an unknown element is shown above. Which of the following correctly identifies the element and provides a valid justification based on the spectrum?"
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date_modified: "2026-08-21T16:02:54+00:00"
---

# The complete photoelectron spectrum of a neutral atom of an unknown element is shown above. Which of the following correctly identifies the element and provides a valid justification based on the spectrum?

The complete photoelectron spectrum of a neutral atom of an unknown element is shown above. Which of the following correctly identifies the element and provides a valid justification based on the spectrum?

![A photoelectron spectrum shown on bare axes without gridlines. The horizontal x-axis is labeled Binding Energy (MJ/mol) with values decreasing from left to right, marked with tick marks at 200, 100, 10, 1, and 0.1. The vertical y-axis is labeled Relative Number of Electrons with tick marks from 0 to 6 at integer intervals. Five solid vertical lines representing peaks appear from left to right: the first peak is located at 193 MJ/mol with a height of 2 units; the second peak is located at 18.7 MJ/mol with a height of 2 units; the third peak is located at 13.5 MJ/mol with a height of 6 units; the fourth peak is located at 1.06 MJ/mol with a height of 2 units; the fifth peak is located at 0.75 MJ/mol with a height of 3 units. No other peaks, labels, text, or annotations appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1787328173-HBWLWs.jpg)

- **A.** The element is \(\text{P}\), because the five peaks correspond to electrons in the \(1s\), \(2s\), \(2p\), \(3s\), and \(3p\) subshells, with the peak at \(0.75\text{ MJ/mol}\) representing the three \(3p\) valence electrons.
- **B.** The element is \(\text{P}\), because the peak at \(193\text{ MJ/mol}\) represents the \(3p\) valence electrons, which require the greatest amount of energy to remove due to being the outermost electrons.
- **C.** The element is \(\text{Al}\), because the five distinct peaks indicate that the atom contains a total of five valence electrons.
- **D.** The element is \(\text{Cl}\), because the rightmost peak at \(0.75\text{ MJ/mol}\) is \(1.5\) times higher than the peak at \(1.06\text{ MJ/mol}\), indicating five valence electrons in that subshell.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/120188/*