Which of these is about the same size and mass as a CARBON proton?
A.
electron
B.
neutron

Neutrons and protons are almost exactly the same size
Explanation:
(a neutron has about 1/10th of one percent more mass). ... Carbon has 6 protons, so its atomic number is 6; oxygen has 8 protons, so its atomic number is 8. Uranium has 92 protons, so its atomic number is 92!