What is the reactivity order of isotopes of hydrogen?

Dear Student,

The natural hydrogen consists of three isotopes:

1. Protium or Ordinary Hydrogen (₁H¹)
2. Deutrium or Heavy Hydrogen (₁H²)
3. Tritium (₁H³)

Tritium is radioactive and therefore least stable. On the other hand, protium is the most stable isotope. Therefore, the increasing order of reactivity will be :
Protium < Deutrium < Tritium
However, protium is more reactive the deutrium as the D-D bond is very strong.
Therefore, the order is
Deutrium < Protium <Tritium