Which of these particles has the greatest mass? (1) alpha (3) neutron

(2) beta (4) positron

(1) alpha is your answer. The alpha particle is a Helium nucleus, with two protons and two neutrons. Therefore its larger than the positron or the neutron (because positrons have around the same mass as the proton, being its anti-particle). The beta particle is just the electron, in which the proton is way more massive than the electron.