TASK DEFINITION: Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
PROBLEM: Fractional crystallization is the separation of compounds on the basis of their solubilities in a given solvent.

SOLUTION: What is the separation of compounds on the basis of their solubilities in a given solvent?

PROBLEM: Radioactivity is the release of particles and/or energy from the nucleus of an atom.

SOLUTION: What is the release of particles and/or energy from the nucleus of an atom described as?

PROBLEM: Elements are pure substances that make up all matter.

SOLUTION:
Elements are pure substances that make up what?