Which of the following is NOT one of the three main parts of an atom?

The three main parts of an atom are protons, neutrons, and electrons. Protons are positively charged particles found in the nucleus of an atom, while neutrons are neutral and also reside within the nucleus, contributing to the atomic mass. Electrons are negatively charged particles that orbit the nucleus in various energy levels.

Quarks, on the other hand, are fundamental particles that make up protons and neutrons. While they are essential components of the particles inside the nucleus, they are not classified as a primary component of an atom itself. Thus, distinguishing quarks from protons, neutrons, and electrons clarifies their role at a more subatomic level, which is why this option does not fit among the main parts of an atom. Understanding these distinctions is crucial for grasping atomic structure in physical sciences and related fields.