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Which hydrogen isotope is called tritium?

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What are isotopes and how do they work? — isotope An overview of isotopes.

Tritium is the hydrogen isotope with a mass number of 3, symbolized as T or 3H. Its nucleus consists of one proton and two neutrons.12

Unlike the stable isotopes of hydrogen, tritium is a radioactive species with a half-life of 12.32 years. While it reacts chemically in a manner similar to ordinary hydrogen, the significant difference in mass between tritium and lighter hydrogen isotopes can lead to distinct chemical properties in the compounds they form.1