Astudent mixes two clear liquids together. after a few minutes, a white powdery solid can be seen settling on the bottom of the test tube. which of the following is a conclusion that the student can draw based on these observations?
a: the two liquids are toxic and should be handled with extreme caution.
b: the two liquids were pure substances before they were mixed.
c: the two liquids have been stored too long and are no longer good.
d: the two liquids have gone through a chemical change in which a new substance called a precipitate was produced.