Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Fractional crystallization is the separation of compounds on the basis of their solubilities in a given solvent.
What is the separation of compounds on the basis of their solubilities in a given solvent?

The properties of the alkali metals are similar to each other as expected for elements in the same family.
The properties of the alkali metals are similar to each other as expected for elements in the same what?

Plants go through seasonal changes after detecting differences in day length.
Plants go through seasonal changes after detecting differences in what?