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

[Q]: Zero is the net force acting on an object when two equal forces are applied from opposite directions.
[A]: What is the net force acting on an object when two equal forces are applied from opposite directions?

[Q]: Collision theory states that chemical reactions occur when atoms, ions, or molecules collide.
[A]: What states that chemical reactions occur when atoms, ions, or molecules collide?

[Q]: Topsoil layer of soil usually does not have very small particles like clay.
[A]:
What layer of soil usually does not have very small particles like clay?