Which of the following correctly illustrates the conservation of mass for the reaction below?

4fe(s) + 3o2(g) → 2fe2o3(s)

In order to apply the principle of conservation of mass to this reaction, we must prove that the mass on the left hand side is equivalent to the mass on the right hand side. In order to do this, we must first acquire the atomic masses of each substance involved. These are:
Fe - 56
O - 16

Now, we substitute these values into the equation:
4(56) + 3(2*16) = 2(56 * 2 + 16 * 3)
224 + 96 = 320
320 = 320

As we can see, the principle of conservation of mass holds true.