Most common isotopes of hydrogen (non-radioactive) is

Protium $\left({ }_1^1 H\right)$ deuterium or heavy hydrogen \left({ }_1^2 \mathrm{H}\right.$or D$)$and tritium \left({ }_1^3 \mathrm{H}\right.$ or T $)$ are the isotopes of hydrogen. Protium or ordinary hydrogen has one proton and no neutron in the nucleus and one electron revolves around the nucleus. It is the most abundant and common form of hydrogen (approximately $99.98 \%$ ). ${ }_1^2 \mathrm{H}+{ }_{\mathrm{l}}^2 \mathrm{H} \longrightarrow{ }_1^3 \mathrm{H}+{ }_1^1 \mathrm{H}$