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

Example Input: Radon is inert and generally unreactive because it is which kind of gas?
Example Output: noble gas

Example Input: Gravitational force on a large scale dominates interactions between large objects because it is always what?
Example Output: attractive

Example Input: What is the separation of compounds on the basis of their solubilities in a given solvent?
Example Output:
fractional crystallization