Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
One example is below.
Q: Earth rotates on its axis once times in one day.
A: How many times does Earth rotate on its axis in one day?
Rationale: The given output correctly poses a question based on the scientific fact given.
Q: The binary halides are an important subclass of salts.
A:
The binary halides are an important subclass of what?