Question

explain why a hot saturated solution of potassium nitrate forms crystals as it cools?

Answer 1

Hot solutions dissolve more of salt, thus a hot solution of potassium nitrate has more salt dissolved as compared to the solution at room temperature. When hot saturated potassium nitrate solution cools, the amount of salt that can remain dissolved in solution reduces. As this happens some of the potassium nitrate begins to precipitate out of solution in the form of crystals. 

Answer 2

When hot saturated potassium nitrate solution cools, the amount of salt that can remain dissolved in solution reduces. As this happens some of the potassium nitrate begins to precipitate out of solution in the form of crystals