The photoelectron spectrum of boron shows three peaks ordered from highest to lowest binding energy with relative areas 2:2:1. What is boron's ground-state electron configuration?

Core Concept

Peak area counts the electrons in a subshell, and binding energy falls with distance from the nucleus. Reading from core outward, the 2:2:1 pattern maps to 1s with two electrons, 2s with two, and 2p with one. Five electrons total matches boron's atomic number, confirming 1s² 2s² 2p¹.