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

Some materials have negative heats of solution; the dissolution of one of these solutes in water is called?
Some materials have negative heats of solution; the dissolution of one of these solutes in water is called?

Protons and neutrons are made of quarks, which are fundamental particles of matter.
A fundamental particle of matter, protons and neutrons are made of these?

Correlation is the comparison of two factors within a population.

What is the comparison of two factors within a population?