What is tritium classified as?

Tritium is classified as a radioactive isotope of hydrogen. It has a nucleus containing one proton and two neutrons, which makes it heavier than the most common hydrogen isotope, protium, which has only one proton. Being a radioactive isotope, tritium undergoes beta decay, emitting radiation and transforming into helium-3 over time.

Tritium is often referred to in contexts related to nuclear reactions, radioluminescent devices, and certain types of research, because it is used in various applications that involve its radioactive properties. Additionally, while it is sometimes associated with heavy water, it is important to recognize that heavy water itself is defined by having deuterium, another isotope of hydrogen, rather than tritium.

The classification as a stable isotope does not apply to tritium, as stable isotopes do not undergo radioactive decay. Similarly, the term "non-radioactive compound" is incorrect since tritium is indeed radioactive. While tritium is sometimes informally called "heavy hydrogen" because of its additional neutrons, the correct scientific classification focuses on its radioactive properties, making "radioactive heavy water" the appropriate choice as it underscores its functionality in specific scientific contexts.