Isotopes of the same element have the same number of protons, but different numbers of neutrons.
- Isotope A has 56 protons.
- Isotope B has 55 protons.
- Isotope C has 57 protons.
- Isotope D has 56 protons.
From this information:
- Isotope A (56 protons, 80 neutrons) and Isotope D (56 protons, 74 neutrons) are isotopes of the same element, as they both have 56 protons.
- Isotope B (55 protons) and Isotope C (57 protons) are not isotopes of A or D, since they have different numbers of protons.
Therefore, Isotopes A and D are the isotopes of the same element.