Answer
Protium: $^1_1$H
one proton, one electron, and no neutrons
Deuterium: $^2_1$H
one proton, one electron, and one neutron
Tritium: $^3_1$H
one proton, one electron, and two neutrons
Work Step by Step
The three isotopes of hydrogen are hydrogen (also known as protium), deuterium, and tritium. All isotopes have the same atomic number, the same number of protons, the same number of electrons, but differing numbers of neutrons.
Protium: $^1_1$H
A neutral atom of regular hydrogen or protium has one proton, one electron, and no neutrons.
Deuterium: $^2_1$H
A neutral atom of deuterium has one proton, one electron, and one neutron.
Tritium: $^3_1$H
A neutral atom of tritium has one proton, one electron, and two neutrons.
