What type of particles do colloids contain?

Colloids are colloidal mixtures that contain particles that are intermediate in size between those found in true solutions and those found in suspensions. In a true solution, the particles are at a molecular or ionic level, typically smaller than a nanometer, allowing them to remain uniformly distributed without settling out over time. In contrast, in a suspension, the particles are larger, usually greater than 1 micrometer, and they will eventually settle out due to gravity if the mixture is allowed to stand.

Colloids consist of particles that range from about 1 nanometer to 1 micrometer in size. This size range allows colloids to remain dispersed in a medium, giving them unique properties such as the Tyndall effect, where they scatter light, distinguishing them from solutions. The intermediate particle size in colloids is crucial to their behavior in various applications, such as in food products, paints, and pharmaceuticals, where stability and uniform distribution are essential. Thus, the correct answer highlights this unique characteristic of colloids regarding particle sizes.