Which particle mediates the strong nuclear force between nucleons inside the nucleus?

The correct answer is Option D — Pion (Pi-meson). Pions (pi-mesons) are responsible for mediating the strong nuclear force between nucleons (protons and neutrons) inside the nucleus. Option A (Gluon): Gluons mediate the strong force at the quark level (inside protons/neutrons), NOT between nucleons directly. Option B (Electron): Electrons mediate electromagnetic force (photon exchange), NOT strong nuclear force. Option C (Neutrino): Neutrinos are involved in weak nuclear force (beta decay), NOT strong nuclear force.