one
Hydrodgen and Oxygen.
Helium has one more proton than hydrogen
In the Earth atmosphere hydrogen exist only as traces: 0,000055 %.
O+H2o+N (oxygen+Hydrodgen 2oxygens+Nitrogen)
air helium hydrodgen carbon dioxide oxygen butane nitrogen argon
Hydrogen is a pure subtance because it is made up of one kind of atom
8 electrons
Hydogen is not a mixture, if it was it wouldn't be on the periodic table, which is a table for all the elements that have been found, elements are made up of one type of atom.
16 electrons
20 electrons
6 electrons
97 electrons