Final answer:
Protons and neutrons are the most similar in mass within an atom, while electrons are significantly lighter.
Explanation:
Protons and neutrons are the two particles most similar in mass within an atom. They both have a mass of approximately 1 atomic mass unit, making them almost equal in mass.
On the other hand, the electron is significantly lighter than both the proton and neutron, with a mass about 1/2000th of a proton or neutron.
Learn more about subatomic particles here:
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