#hydrogen_atom  an atom of hydrogen
  supertype:  #atom  (physics and chemistry) the smallest component of an element having the chemical properties of the element
  part:  #hydrogen_ion
  subtype:  #acidic_hydrogen__acid_hydrogen  a hydrogen atom in an acid that forms a positive ion when the acid dissociates
  subtype:  #deuterium__heavy_hydrogen__heavyhydrogen  an isotope of hydrogen which has one neutron (as opposed to zero neutrons in hydrogen)

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