TASK DEFINITION: Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
PROBLEM: Seismic waves prove the inner core it is solid.

SOLUTION: What do seismic waves prove about the inner core?

PROBLEM: Ionic compounds contain cations and anions rather than discrete neutral molecules.

SOLUTION: Ionic compounds contain cations and anions rather than what?

PROBLEM: In an electromagnetic wave, the crests and troughs represent oscillating fields.

SOLUTION:
In an electromagnetic wave, what do the crests and troughs represent?