There are three known generations of quarks (up and down, strange and charm, top and bottom) and leptons (electron and its neutrino, muon and its neutrino, tau and its neutrino), with strong indirect evidence that a fourth generation of fermions does not exist.
The,re are three known generations of quarks (up and ,down, strange and charm, top and bottom) and leptons (electron and its neutrino muon and its neutrino tau and its neutrino), with strong indirect evidence that a fourth generation of fermions does not exist.