#### Answer

a. The proportion of mass of iron to mass of oxygen is the same for all four samples. We see this because the four samples form a linear function. For every gram of oxygen, there are approximately 2.5 grams of iron. Thus, since the ratio between the two elements is the same for all the samples, we agree that the four samples are the same compound.
b. In the new sample we have 9.9 grams of iron and 3.4 grams of oxygen. This means that for each gram of oxygen, we have roughly 2.9 grams of iron. This ratio is differs considerably from the ratio of the other four samples (2.6 g Fe/ 1 g Oxygen). Therefore, the new sample is not the same substance as the other four samples.