Multiple choice Which of the following is the heaviest subatomic particle? Electron Proton Neutron Photon Reveal answer Fill a bubble to check yourself C Correct answer Explanation Neutron is the heaviest subatomic particle. Neutron is 1842 times heavier than an electron. Mass of neutron is 1.0086654 a.m.u. or 1.6749 x 10-27 kg.