Multiple choice

The most massive and solid part of the atom is ___________.

  1. proton

  2. electron

  3. neutron

  4. nucleus

Reveal answer Fill a bubble to check yourself
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.