Final answer:
Without additional context, Option 3 stands as the most universally true statement; it asserts the two nuclei are not isotopes of the same element, which is consistent with isotopes having the same atomic number but different mass numbers.
Step-by-step explanation:
The correctness of the provided options about the two nuclei can be established based on the definition of atomic number, mass number, and isotopes:
- The atomic number (Z) represents the number of protons in the nucleus and defines the identity of an element.
- The mass number (A) is the sum of the numbers of protons and neutrons in the nucleus.
- Isotopes are nuclides that have the same atomic number but different mass numbers due to variations in their number of neutrons.
Given these definitions:
- Option 1 is incorrect because the statement about the same atomic mass does not constitute a concrete claim without additional context.
- Option 2 could be true if the context implies adding up atomic numbers, but that's not typically how atomic numbers are discussed, so this option is likely incorrect.
- Option 3 is true if the nuclei have different atomic numbers, as isotopes must have the same atomic number but can have different mass numbers.
- Option 4 is true only if the nuclei have identical numbers of protons, which defines them as the same element.
Without more specifics about the two nuclei being discussed, it's difficult to definitively state which option is true, but we can infer based on the information provided. The statement that would most universally be considered true, given the definition of isotopes, is Option 3: They are not isotopes of the same element, assuming the two nuclei have different atomic numbers.