Which total mass is the smallest?
(1) the mass of 2 electrons
(2) the mass of 2 neutrons
(3) the mass of 1 electron plus the mass of 1 proton
(4) the mass of 1 neutron plus the mass of 1 electron

The mass of electrons, protons, and neutrons:
electrons 9.10938291*10^-31 kg
protons 1.67262178*10^-27 kg
neutrons 1.6749*10^-27 kg
the mass of electrons is way smaller than both, the mass of protons and neutrons
therefore, 1) the mass of 2 electrons is the smallest

D.na is the answer hope this