Isotopes are variants of atoms of a particular chemical element. They still have the same number of protons (and belong to the same element), but they have different number of neutrons.

The Hydrogen has three isotopes:  {}_{1}^{1}H,\text{ }{}_{1}^{2}\text{H, }{}_{1}^{3}\text{H}

Protium,  {}_{1}^{1}H

Is the most common hydrogen isotope with an abundance of more than 99.98%. This is the only isotope without neutron.

Deuterium, {}_{1}^{2}\text{H}

The other stable hydrogen isotope, 0.015%, is not radioactive and has insignificant toxicity hazard. When is part of the water instead of the normal hydrogen, forms the heavy water.

Tritium, {}_{1}^{3}\text{H}

Contains one proton and two neutrons in its nucleus. It is radioactive, but exist because of the interaction of cosmic rays with atmospheric gases.

There are more hydrogen isotopes, but they are synthesized in the laboratory, and they are highly unstable.

Carbon Isotopes are   {}_{6}^{12}C,\text{ }{}_{6}^{13}\text{C, }{}_{6}^{14}\text{C}

With that information you should know:

  1. The atomic number of the Carbon
  2. The number of protons, and electrons
  3. Which one is the heaviest one?, and How many neutrons has?