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
In beta particle emission, a neutron in the nucleus converts into a proton, an electron (beta particle), and an antineutrino.
This particle is the neutron.
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....
The largest subatomic particle (by mass) is the proton. The mass of subatomic particles is measured in atomic mass units (amu). The proton has a mass of 1.007 amu, the neutron has a mass of 1 amu, and the electron has a mass of .0005 amu.