Question

why deuterium is called as heavy hydrogen ? why not tritium ?

Answer 1

Probably because tritium has another more dramatic property that deuterium doesn’t: it’s unstable.
It decays with a half-life of 12.32 ± 0.02 years into helium-3, an electron and an electron antineutrino.

This was answered by a great person and I wrote it here.

Answer 2

duetrium also called heavy hydrogen becoz itz one of two stable isotopes of hydrogen as it contains one proton and one neutron also duetrium is non radio active and non toxic while tritium is unstable isotope , radio active, toxic one