Final answer:
Oxygen-16 and Oxygen-18 are isotopes of oxygen with 8 protons each but differing in the number of neutrons, with Oxygen-16 having 8 neutrons and Oxygen-18 having 10 neutrons. They are stable isotopes and occur in oxygen with natural abundances of 99.76% and 0.20% respectively.
Step-by-step explanation:
The two forms of oxygen mentioned, Oxygen-16 and Oxygen-18, are called isotopes. Isotopes are different forms of the same element that have the same number of protons but a different number of neutrons. In this case, both isotopes have 8 protons since the atomic number of oxygen is 8. Oxygen-16 has 8 neutrons, and Oxygen-18 has 10 neutrons. Isotopes of all naturally occurring elements are present in nearly fixed proportions that constitute an isotope's natural abundance. For instance, naturally occurring oxygen is majorly composed of Oxygen-16, with a natural abundance of 99.76%. Oxygen-18, which makes up about 0.20%, is not radioactive, meaning both Oxygen-16 and Oxygen-18 are stable isotopes.
Isotopes are different forms of the same element that have the same number of protons, but a different number of neutrons. In the case of oxygen, the isotope with 8 protons and 8 neutrons is called oxygen-16, and the isotope with 8 protons and 10 neutrons is called oxygen-18. These different forms of the same element have slightly different properties due to the difference in the number of neutrons.