Which of the following vary for isotopes of atoms of the same element? A. Atomic number
B. Atomic mass
C. Number of electrons
D. Number of protons

Atomic mass because “Different isotopes of the same element have the same atomic number. They have the same number of protons.” and it cant be electrons since they’re equal to protons and in isotopes only neutrons are differnet. “Isotopes are atoms with different atomic masses which have the same atomic number.”