

- This is a vial containing ultrapure hydrogen gas. Hydrogen is a colorless gas that glows violet when ionized.Wikipedia Creative Commons License

- Protium is the most common isotope of the element hydrogen. Protium has one proton and one electron, but no neutrons.Blacklemon67, Wikipedia Commons

- NGC 604, a region of ionized hydrogen in the Triangulum Galaxy.Hubble Space Telescope, photo PR96-27B