How nucleus of oxygen-18 atom is different from the nucleus of an oxygen-16 atom?
Any oxygen atom has exactly 8 protons in its nucleus–this number cannot change as it is what defines the element as oxygen–if this number changed, the atom would become a different element. Oxygen-16 and Oxygen-18 are isotopes of oxygen. Isotopes are atoms of the same element (and thus the same number of protons–atomic number) but different number of neutrons (different mass number). Oxygen-16 has 16 nucleons in its nucleus (8 protons and 8 neutrons–a standard oxygen atom), but oxygen-18 has 18 nucleons in its nucleus (8 protons and 10 neutrons–a different isotope of oxygen). Hope this helps!
