Which Answer Choice Correctly Describes Why The Isotope Oxygen 18 18o Is Differe

Which answer choice correctly describes why the isotope oxygen-18 (18O) is different from the isotope oxygen-16 (16O)? Its atomic number is different because it has two more neutrons. Its atomic number is different because it has two more protons. Its atomic mass is different because it has two more protons. Its atomic mass is different because it has two more neutrons.