What is the significance or purpose of having extra nuetron in element hydrogen during nuclear fission?

Answer 1

The significance is in nuclear fusion (H-bombs and the sun), not nuclear fission (A-bombs and power reactors). Two deuterons, heavy hydrogen, each having one proton and one neutron, join together to produce one helium nucleus, having two protons and two neutrons. Without at least one neutron in a deuteron, helium could not form.