- Option 1: Same mass number - This is incorrect. Isotones do not have the same mass number; they have the same number of neutrons but different mass numbers, because the number of protons (and thus the atomic number) is different.
- Option 2: Same atomic number - This is incorrect. Isotones are atoms of different elements, so they must have different atomic numbers (the number of protons). Having the same atomic number refers to isotopes, not isotones.
- Option 3: Same number of neutrons - This is the correct answer. Isotones are atoms of different elements that have the same number of neutrons but different atomic numbers (and thus different mass numbers).
- Option 4: Same number of electrons - This is incorrect. The number of electrons in isotones can vary depending on the ionization state, and it is not a defining characteristic of isotones.
Explanation:
Isotones are atoms of different elements that have the same number of neutrons but different atomic numbers and mass numbers. For example, carbon-14 (C-14) and nitrogen-15 (N-15) are isotones because they both have 8 neutrons, but they differ in the number of protons (atomic number) and thus belong to different elements.