Question

what is the particle that is labeled with a question mark (?) in the diagram?
beta particle
quark
isotope
alpha particle

Explanation:

Protons and neutrons are made up of quarks. Beta - particles are high - energy electrons or positrons. Isotopes are atoms of the same element with different numbers of neutrons. Alpha - particles are helium nuclei. Since protons and neutrons are composed of quarks, the particle in question within the proton is a quark.

Answer:

quark