Given a scientific question, generate a correct answer to it.

Ex Input:
What is the term for the movement of molecules from an area of high concentration to an area of low concentration?

Ex Output:
diffusion

Ex Input:
What are the ionic compounds that produce negative hydroxide ions when dissolved in water?

Ex Output:
bases

Ex Input:
What properties describe the existence of matter, as opposed to chemical properties that describe how substances change into other substances?

Ex Output:
physical