Which is NOT fundamental particle

A Neutron is not a fundamental particle. According to the Standard Model of particle physics, fundamental particles are those that are not made up of smaller constituents. Neutrons (and protons) are composite particles known as baryons, which are in turn composed of even smaller, more fundamental particles called quarks. Specifically, a neutron is made up of one "up" quark and two "down" quarks (udd). Therefore, it is a composite particle, a type of hadron, rather than an elementary or fundamental particle. Understanding this distinction is crucial in subatomic physics.

• Proton: Like neutrons, protons are also composite particles, made up of quarks (specifically, two "up" quarks and one "down" quark, uud). Thus, protons are also not fundamental particles. However, in this multiple-choice context where only one answer can be selected as "NOT fundamental", Neutron is designated as the correct choice.
• Neutrino: Neutrinos are fundamental particles. They are a type of lepton, which are elementary particles that do not interact via the strong nuclear force. They are considered indivisible in current particle physics.
• Quark: Quarks are fundamental particles. They are elementary fermions and are the fundamental constituents of hadrons, such as protons and neutrons. There are six types (flavors) of quarks, each having a fractional electric charge.