The correct answer is Tritium.
Here's why:
- Isotopes of Hydrogen: Hydrogen has three isotopes:
- Protium (Hydrogen): 1H (1 proton, 0 neutrons). It is the most common and stable isotope of hydrogen and is not radioactive.
- Deuterium: 2H or D (1 proton, 1 neutron). It is a stable, non-radioactive isotope of hydrogen. It is used in nuclear magnetic resonance (NMR) spectroscopy as a solvent. Heavy water (D2O) is water in which the hydrogen atoms are replaced by deuterium.
- Tritium: 3H or T (1 proton, 2 neutrons). Tritium is a radioactive isotope of hydrogen. Its nucleus is unstable and decays through beta decay.
- Radioactivity: Tritium undergoes beta decay, emitting an electron and an antineutrino, and transforming into helium-3:
Therefore, Tritium is the only radioactive isotope among the options.
Correct Answer: Tritium