Answers:
Protium = ¹₁H = Hydrogen-1
Deuterium = ²₁H = Hydrogen-2
Details:
Isotopes are the variants of elements in which the element has same number of protons but different number of neutrons which results in different mass number for the same element.
Examples:
Hydrogen-1 (¹₁H) has one proton and one electron. It lacks neutron hence it has a mass number of 1.
Hydrogen-2 (²₁H) has one proton, one electron and one neutron. Hence, it has a mass number of 2.
Below the attached figure shows the two isotopes of Hydrogen. The black spheres show electrons, red spheres show protons while blue sphere represent neutrons.
