"Solidifying" is the antonym for becoming liquid. Solidifying refers to the process of converting a liquid into a solid state. When a substance is becoming solid, its molecules are slowing down, losing energy and coming closer together, which makes the substance more rigid and harder to deform. This occurs when a liquid is cooled below its freezing point, or when a chemical reaction causes it to crystallize or become solid. Some examples of substances that can solidify include water, butter, concrete, and molten metals. Solidification is an important process in many areas of science, including materials science, chemistry, and geology.