What are smaller sub-particles of the proton and neutron called?

Quarks are fundamental particles that serve as the building blocks for protons and neutrons, which are components of atomic nuclei. Each proton and neutron is made up of three quarks bound together by the strong force, which is mediated by particles called gluons. Quarks come in different types, known as "flavors," including up, down, charm, strange, top, and bottom, and the specific combination of quarks determines the properties of the proton or neutron.

In contrast, electrons are elementary particles that orbit the nucleus of an atom, molecules are made up of two or more atoms bonded together, and atoms themselves are the basic units of matter. Thus, quarks specifically refer to the smaller sub-particles that make up protons and neutrons, making it the most accurate choice.