Which school-level mass comparison for nuclear particles is appropriate?
A proton has negligible mass but a neutron has one unit.
Both have the tiny mass associated with an electron.
A proton and a neutron are each about one unified atomic mass unit.✓Richtige Antwort
A neutron has no mass because it has no charge.
Erklärung
Both protons and neutrons have masses close to one unified atomic mass unit at school-level precision. A neutron's lack of electric charge does not make its mass vanish, and electron mass is far smaller.