What indicates that two atoms are isotopes of each other?

Isotopes of an element are defined as atoms that have the same number of protons but differ in the number of neutrons. The number of protons in an atom, also known as the atomic number, determines the identity of the element. Therefore, if two atoms have the same number of protons, they are indeed isotopes of the same element, regardless of the number of neutrons they possess.

Since isotopes maintain the same atomic number (indicating they are the same element), this allows for variations in their mass due to the differing neutron counts. Consequently, it is their shared number of protons that fundamentally categorizes them as isotopes of each other. Understanding this relationship is essential in distinguishing between different isotopes and their respective physical and chemical properties.