You transfer a clear liquid from a beaker into a test tube. You heat the test tube with the unknown liquid over a Bunsen burner. The liquid begins to vaporize and after continued heating a white crystalline material is all that remains in the test tube. The test tube initially contained:
a compound
a mixture
an element
a solution

A mixture

Explanation: I don't really have one I just know and i just can't explain it

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.