Question

One amu is equal to

the mass of an electron
the mass of one proton or one electron
the mass of one neutron or one electron
the mass of one neutron or one proton

Answer 1

Answer is: the mass of one neutron or one proton.
Unified atomic mass unit is a standard unit of mass, that quantifies mass on an atomic or molecular scale (atomic mass). One unified atomic mass unit is approximately the mass of one nucleon (proton or neutron).