Hydrogen is a chemical element with chemical symbol H and atomic number <answer>1</answer>. With an atomic weight of 7000<answer>1</answer>00794000000000♠<answer>1</answer>.00794 u, hydrogen is the lightest element on the periodic table. Its monatomic form (H) is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass.[note <answer>1</answer>] Non-remnant stars are mainly composed of hydrogen in its plasma state. The most common isotope of hydrogen, termed protium (name rarely used, symbol <answer>1</answer>H), has one proton and no neutrons.
What is the atomic number used for hydrogen?
1