What characteristic is true for liquids regarding their volume and compressibility?

Liquids are characterized by having a definite volume that does not change significantly under pressure, which is why they are often considered incompressible. While they do allow for some changes in shape based on the container they occupy, their volume remains relatively constant. In addition, the particles in a liquid are in constant random motion, which allows for the fluidity that defines liquids. This random movement facilitates the ability of liquids to flow and take the shape of their containers, further supporting the idea of incompressibility.

The notion of liquids being incompressible adds to their unique properties in contrast to gases, which are highly compressible and can fill a larger volume when pressure is applied. The distinction regarding diffusion is also relevant; while liquids can mix and diffuse over time, they do not exhibit 'no diffusion' as stated in one of the options. Hence, the correct characterization of liquids involves understanding that they are incompressible and exhibit constant random movements, making option C the most accurate description.