Question

when a substance changes from a gas into a liquid, what has happened? heat has been removed. heat has been added. the molecules have sped up. the molecules have formed crystals.

Explanation:

The process of a gas changing to a liquid is condensation. Condensation occurs when heat is removed from the gas, causing the gas molecules to lose energy, slow down, and come closer together to form a liquid. Adding heat (option B) would cause a liquid to gas (vaporization). Molecules speeding up (option C) is associated with adding heat (increasing energy), not condensation. Forming crystals (option D) is related to solidification (liquid to solid), not gas to liquid. So the correct answer is the option where heat is removed.

Answer:

A. Heat has been removed