Final answer:
A white solid forming at the bottom of a container after mixing two liquids signifies a chemical change, as a new substance has been created.
Step-by-step explanation:
When a student mixes two liquids together and observes that a white solid has formed at the bottom of the container, they can conclude that a chemical change has occurred. This conclusion is drawn from the evidence that a new substance (a precipitate) has been formed, which is a common indicator of a chemical change. Chemical changes involve the transformation of one substance into another at the molecular level, which can be evidenced by changes such as the formation of a precipitate, a color change, the production of gas, or temperature change.