Correct Answer: Isotopes

Solution : The correct answer is Isotopes.

Isotopes are those atoms which have the same number of protons but different numbers of neutrons.

For example- There are three isotopes of Hydrogen. They are Protium, Deuterium, and Tritium. Where Protium only has one electron and one proton, Deuterium has one electron, one proton, and one neutron, while Tritium has one electron, one proton, and two neutrons.