19. Balance the following chemical equation: Fe + O2 → Fe2O3 What is the coefficient on Fe, O2 and Fe2O3? *

a. 1, 2, 3

b. 4, 3, 2

c. 1, 3, 1

d. 2, 1, 1

20. The law of conservation of mass lets us know that in every chemical equation you have to have the same number of ________ on both sides of the equation. *

a. moles

b. coefficients

c. atoms of each element

d. molecules