Radioactive elements emit $\mathrm{\alpha }$$\mathrm{\beta }$ , and $\mathrm{\gamma }$ rays and are characterized by their half-lives. The radioactive isotope of hydrogen is

1. Protium

2. Deuterium

3. Tritium

4. Hydronium

Hint: Isotope having an atomic mass of 3 is radioactive.

The radioactive isotope of hydrogen in tritium. For tritium (n=3, p=1), therefore n/p ratio is 3.