What characteristic do isotopes share?

Isotopes are variants of a particular chemical element that share the same number of protons in their atomic nuclei. This is what defines them as the same element, regardless of the differences in the number of neutrons they possess. Because the number of protons determines the identity of the element, isotopes will have the same chemical properties and behavior in reactions.

While options regarding neutrons or energy levels may refer to specific atomic properties, they do not apply universally to all isotopes. For example, isotopes of the same element can differ in neutron count, affecting their mass but not their chemical reactivity. Thus, understanding that isotopes have the same number of protons provides a fundamental basis in chemistry and nuclear physics, highlighting their shared identity as distinct forms of the same element.