What type of particles are classified as quarks?

Quarks are classified as fractionally charged particles that experience all the fundamental forces of nature, including the strong nuclear force, which binds them together to form protons and neutrons. Each quark possesses a charge of either +2/3 or -1/3, allowing them to combine in various ways to create particles such as baryons (e.g., protons and neutrons) and mesons (which are made of quark-antiquark pairs).

The fact that quarks are affected by all fundamental forces highlights their role in the strong interaction that holds atomic nuclei together, as well as in the electromagnetic and weak interactions. Since quarks are confined within hadrons and cannot exist freely due to the phenomenon known as color confinement, they are integral to the structure of matter itself.

In contrast, other options do not accurately describe quarks. For instance, quarks are indeed affected by fundamental forces, unlike elementary particles that might not interact with them, and they cannot exist independently, as stated in the other choices. The correct understanding emphasizes their fractional charge and their interaction with all fundamental forces, which is essential for understanding particle physics and the building blocks of matter.