Answer choices are : d two chemist are trying to determine if their water sample is a mixture or pure substance. in their investigation they first filter the sample of dirty water with gravel. the water is then clearer than before. see image. what does this change tell the chemist about the chemical make up of the sample? a. the water before filtration is a pure substance, because the particles did not maintain their chemical properties. b. the water before filtration is a mixture because the particles could be physically separated. c. more information is needed to answer the question. d. the water before filtration is a mixture because it cannot be physically separated and must be chemically separated.