hydrgen nucleus
neutron, but only in the isotope H-1 (protium)
The pair form a hydrogen atom.There is a fallacy that's taught about this pairing, which is that the electron-proton pair form a neutron. See my answer to the question "What particle has the same mass as a hydrogen atom?" for more details about this, and why it is wrong.
Electron, proton, nucleus, atom
This particle is the neutron.
In beta particle emission, a neutron in the nucleus converts into a proton, an electron (beta particle), and an antineutrino.
Electron!
Hydrogen usually has no neutrons. However, there is also the heavy hydrogen, a.k.a. deuterium, that has both a proton and a neutron in its nucleus.
Neutron
Yes. The electron is the smallest whole particle.
The isotope hydrogen-1 don't contain neutrons.
among these Electron has the least mass....
Ion.