Classify each of the following as either a lepton or a hadron: electron, proton, neutron, pi meson, electron neutrino, muon neutrino, tau neutrino.
Protons, neutrons and pi mesons are members of the hadron family of particles. Hadrons are particles that interact through the strong force.

Electrons, electron neutrinos, muon neutrinos and tau neutrinos are members of the lepton family. Leptons interact through the weak force, and if charged, the electromagnetic force.