The most massive and solid part of the atom is ___________.
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proton
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electron
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neutron
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nucleus
D
Correct answer
Explanation
The nucleus contains protons and neutrons (collectively called nucleons), which account for over 99.9% of an atom's mass. Electrons orbit the nucleus and have negligible mass (about 1/1836 of a proton). Therefore, the nucleus is both the most massive and solid (densest) part of the atom.