American Chemical Society (ACS) Chemistry Test 2025 – 400 Free Practice Questions to Pass the Exam

The correct choice highlights that electrons occupy most of the atomic volume. In an atom, the nucleus, composed of protons and neutrons, is very small compared to the entire atom. The protons and neutrons are densely packed in the nucleus, contributing only to a tiny fraction of the total atomic volume.

In contrast, electrons are located in orbital clouds surrounding the nucleus. These orbitals represent regions in space where there is a high probability of finding an electron. The spatial distribution of these electron clouds can extend far from the nucleus, encompassing a significant volume around it. Thus, despite being much less massive than protons or neutrons, electrons are responsible for the majority of the atomic volume due to the extensive areas they occupy in their various energy levels.

This understanding aligns with the fundamental model of atomic structure where the nucleus serves as a compact center surrounded by a relatively large and diffuse cloud of electron density.