1. Protium, as an element (or elemental), is one of hydrogen isotopes, as one of the main stable isotopes of hydrogen and as one of the most important elements in the universe. One of the isotopes of hydrogen, the symbol H, has an atomic mass of 1, and its atoms, composed of a proton and an electron, are the main components of hydrogen. Regular hydrogen contains 99.985% hydrogen.

2. Deuterium, an isotope of hydrogen with an atomic weight twice that of ordinary light hydrogen, is found in small amounts in natural water, used in nuclear reactions, and as a tracer in chemical and biological research. Deuterium is a stable isotope of hydrogen, also known as deuterium, with the element symbol D or 2H. Mass number 2. Its nucleus consists of a proton and a neutron. The natural content is about 7, 000 times that of normal hydrogen, used in thermonuclear reactions.

3. A radioactive isotope of hydrogen with an atomic weight three times that of ordinary hydrogen. It has a half-life of 12.5 years and forms helium with a mass of 3 when it disintegrates in beta rays. Tritium is produced by bombarding lithium with neutrons. One of the isotopes of hydrogen, called "superheavy hydrogen". Sign T, mass number 3. It's radioactive. Extremely small in nature, produced by nuclear reactions. Mainly used in thermonuclear reactions.