A. tritium
B. deuterium
C. protium
D. ortho-hydrogen
A. tritium
Tritium is a radioactive isotope of hydrogen. It has the same number of protons as normal hydrogen (1 proton), but it has two neutrons instead of just one, giving it a different atomic weight (3 instead of 1). Tritium is radioactive, which means that it undergoes decay over time and emits high-energy particles. This makes it useful in a number of applications, such as in nuclear weapons and in tritium light sources, which are used to illuminate various devices. However, it also poses some dangers, as tritium can be harmful if it is ingested or inhaled in large quantities.