What are smaller sub-particles of protons and neutrons called?

Quarks are the fundamental building blocks that combine to form protons and neutrons, which are known as nucleons. Specifically, protons are made up of three quarks, while neutrons are also composed of three quarks, held together by the strong nuclear force mediated by particles called gluons. This makes quarks essential for understanding the structure of matter at a subatomic level.

In contrast, electrons are a different type of subatomic particle that exists outside of the nucleus of an atom and carry a negative charge. Neutrinos are very light and neutral particles that rarely interact with matter and are not constituents of protons or neutrons. Atoms, which represent the basic units of chemical elements, are made up of a nucleus (containing protons and neutrons) surrounded by electrons, but they are not sub-particles of protons or neutrons themselves. Thus, quarks are indeed the correct answer as they directly relate to the internal structure of protons and neutrons.