Respuesta :
Answer:
D. The mass number
Explanation:
Isotopes are defined for same atoms
If an atom has same number of protons and same number of electrons but different number of neutrons in it then such pair of atoms is known as isotopes
so we have
same atomic number in all isotopes
since atomic number is same so we can say that total charge of the two atoms must be same
So we will say that since number of neutrons is different in isotopes to sum of neutrons and protons which is known as mass number is different in such pair of atoms
So correct answer is
D. The mass number