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

Q: A collapsing nebula leads to nuclear fusion process.

A: A collapsing nebula leads to what process?
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Q: Monatomic ions form when a single atom gains or loses electrons.

A: What form when a single atom gains or loses electrons?
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Q: Weight is the measure of the force of gravity pulling down on an object.

A:
What is the measure of the force of gravity pulling down on an object called?
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