Answer: Photosynthesis and cellular respiration are related because the reactants for photosynthesis is the products (plus ATP) is cellular respiration. Also the products for cellular respiration is the reactants for cellular respiration.
Oxygen is the 8th element in the periodic table. This means that oxygen has 8 protons and 8 electrons. In order to get the number of neutrons you take the atomic weight in this case 15.9999~16 and you subtract it by the number of protons (16-8).