A student was given two clear liquids; a colorless liquid and a dark-blue liquid. The student was asked to combine the liquids in a beaker and record observations. Which of the following results, if true, would provide the best evidence that a chemical change took place when the liquids were combined?
a. have combined to produce a new substance.
b. were pure substances before they were mixed.
c. are toxic and should be handled with extreme caution.
d. have been stored too long and are no longer good.

A chemical change is one in which a new substance is formed. To check if there is a chemical change when the two liquids were combined, what we simply need to do is to see if there is the formation of a new substance. The new substance formed is expected to be chemically and physically distinctive from its formative members.

B is incorrect

Being pure or impure does not provide any information if a chemical change had occurred or not.

C is incorrect

The toxicity of both doesn’t provide any information as regards if a chemical change had occurred or not

D is incorrect.