When we have atoms with the same quantity of protons but not of neutrons we have: * Isobars
Isoatoms
Isotopes
Isotones

Atomic mass is an average number of the mass number of the atoms of the nature, if we have an element with an atomic mass in the periodic table of 58.933, we can say that most of its atoms would have a mass number of *

58
57
59
58.5