There are 36 quarks in the nucleus of a carbon-12 atom. The nucleus consists of six protons and six neutrons, each of which has three quarks. Each proton has two “up” quarks and one “down” quark, while each neutron has two “down” quarks and one “up” quark.References:”Nelson Modular Science, Volume 3″; Lesley Butcher, Philip Eastwood, Averil Macdonald; 2002.”Elementary-Particle Physics: Revealing the Secrets of Energy and Matter”; National Research Council Committee on Elementary-Particle Physics; 1998.Resources:”Quarks, Leptons and the Big Bang”; Jonathan Allday; 2002.