Final answer:
To determine the mass of oxygen combined with the iron, divide the mass of the iron nail by the molar mass of iron, use the molar ratio from the balanced chemical equation to find the number of moles of oxygen, and multiply the number of moles of oxygen by the molar mass of oxygen.
Step-by-step explanation:
To find the mass of oxygen combined with the iron, we need to determine the molar ratio of iron to oxygen. First, we find the molar mass of iron, which is 55.8 g/mol. If the mass of the iron nail increases to 28.1 g, we divide this mass by the molar mass of iron to determine the number of moles of iron. Next, we use the molar ratio from the balanced chemical equation to find the number of moles of oxygen. Finally, we multiply the number of moles of oxygen by the molar mass of oxygen to find the mass of oxygen combined with the iron.