Which particles have almost the same mass?
proton and electron
proton and neutron
electron and neutron
all three particles
Proton and the Neuron are almost the same mass
Protons and Neutrons are effectively the same particle.
A proton is made from two up quarks and one down quark.
A neutron is made from one up quart and two down quarks.
They have almost identical masses.
Electrons fly around the outside of the atoms' nucleus, which is made from protons and neutrons, and have a much much smaller mass.