When a liquid is cooled, the kinetic energy of the particles decrease and the space between the particles also decrease, and the matter changes its state to solid.
Step-by-step explanation:
Liquid is the state of matter which is one of the fluid, and its denser than gases but rarer than solids. The particles of liquid have a particular amount of kinetic energy which depends on the temperature of the liquid. As the temperature is decreased, the energy content of the matter as a whole decreases. This in turn, decrease the energy levels of individual molecules, and the kinetic energy of the molecule also decrease.
As the kinetic energy of the molecules decrease, the collision between the molecules decrease. This brings the molecules closer, binding them into the van der Waal's force. Thus they condense into solids.