Answer: Option (a) is the correct answer.
Step-by-step explanation:
In gaseous state, molecules move rapidly from one place to another as the molecules have high energy.
So, when gaseous state changes into liquid state then molecules slow down in speed because of decrease in energy molecules come slightly closer to each other.
For example, during condensation of water, vapors change into liquid.
Thus, we can conclude that energy must be removed because particles in liquid move more slowly best describes the transition from gas to liquid.