The mass of an electron is

a) higher than the mass of the proton or the neutron

b) not significant to the overall mass of the atom

c) equal to the mass of the proton and the neutron

not significant to the overall mass of the atom

Explanation:

The mass number of an atom is the combination of the mass of the protons and neutrons.  Electrons are not included because their mass are so insignificant that is doesn't change the total mass much, therefore they are left out. The mass of an electron is about 1,830 times smaller than protons and neutrons.