Final answer:
option d,Isotopes are atoms with the same atomic number but different mass numbers. The mass number is the total number of protons and neutrons, while the atomic mass accounts for this in atomic mass units.
Step-by-step explanation:
The mass number is related to (but not equivalent to) the atomic mass. The correct answer to the question is D. Isotope.
Each element is defined by a unique atomic number (number of protons) and atomic mass. For example, carbon (C) has an atomic number of 6 and a common isotope with a mass number of 12 Da, derived from the sum of 6 protons and 6 neutrons. The atomic mass unit (amu) is essential in measuring this mass, being approximately the mass of one proton or neutron. Isotopes are atoms of the same element that have the same atomic number but different mass numbers, due to varying numbers of neutrons.
To determine the number of protons, neutrons, and electrons: the atomic number (Z) provides the number of protons (and in a neutral atom, electrons as well), and the mass number (A), which equals the sum of protons and neutrons (N), can be used to find the neutron count (A = N + Z).