Tritium is an isotope of hydrogen whose nucleus Triton contains 2 neutrons and 1 proton. Free neutrons decay into
. If one of the neutrons in Triton decays, it would transform into He3 nucleus. This does not happen. This is because
When the tritium is brought into radioactive decay the equation formed is
where
e is a subatomic particle; electron, 
is electron neutrino a subatomic lepton particle with a net electrical charge equal to zero.
As the question given, the isotope of Tritium has an atomic number of 1 and atomic weight of 3, which means the number of proton in an isotope of tritium, is 1. Now as the question says that the element tritium decays so after decay of tritium the nucleus that contained 1 protons and 2 neutron will change into 
i.e. 2 protons and 1 neutron, and an energy release of 
, which is distributed in an average of 
with the rest of the energy is taken by the electron antineutrino. Now due to beta decay the reaction generates low energy, Thereby, making tritons energy less than that of a 
nucleus.