What is the main characteristic of a 'Colloidal' substance?

A colloidal substance is characterized by its gel-like properties due to the presence of small particles that are dispersed within a continuous medium. This dispersion prevents the particles from settling out, resulting in a mixture that appears uniformly distributed at a microscopic level but can exhibit different properties at a macroscopic level.

Colloids can take on various forms, including foams, emulsions, and gels, and they demonstrate unique behaviors such as the Tyndall effect, where light is scattered by the dispersed particles, making them visually distinct. This gel-like quality is essential, as it illustrates how colloids maintain a stable structure that can support a collection of dispersed particles, leading to their versatility in various applications, from food products to pharmaceuticals.

The other options, such as crystalline, homogeneous, and uniform, do not adequately capture the essence of colloids. Crystalline refers to a solid structure with a defined arrangement of atoms or molecules, whereas homogeneous primarily describes a mixture that is consistent throughout. Uniform implies an even distribution, but it doesn’t encapsulate the distinctive characteristics that give colloids their unique properties, particularly their gel-like nature.