In this synthesis reaction, iron and sulfur combine to form iron(II) sulfide, FeS. The balanced chemical equation is:
Fe (s) + S (s) → FeS (s)

When 431 g of iron reacted with sulfur, a total of 502 g of iron(II) sulfide was formed. Based on the reaction stoichiometry, 678 g of iron(II) sulfide should have been produced. What is the mass of 502 g known as?
A. Actual yield
B. Percent composition
C. Theoretical yield
D. Percent yield