Which term describes a mixture where the dispersed phase particles are smaller than in suspensions but larger than those in solutions, forming colloidal dispersions?

• A. Suspension
• B. Solution
• C. Nonelectrolyte
• D. Colloids

Answer: (D)

The key idea is how the size of the dispersed particles determines the type of mixture and its behavior. In a true solution, the dissolved particles are so tiny—molecular or ionic scale—that light passes through without scattering and the distribution is uniform, with no settling over time. In a suspension, the dispersed particles are large enough to be seen and will settle out under gravity, often needing stirring or filtration to separate them. Colloids sit between these two extremes: the dispersed particles are smaller than in suspensions but larger than in solutions, typically in the nanometer to submicron range. Because they are in this intermediate size, they scatter light (the Tyndall effect) and remain dispersed for a long time due to Brownian motion and protective interactions that prevent rapid aggregation. This is why the term that describes such mixtures is colloids—colloidal dispersions where the particles are large enough to affect light but small enough to stay suspended. Examples include milk, fog, and gelatin, which help illustrate how the dispersed phase interacts with the medium to form a stable, spread-out mixture. The other terms don’t fit this size-based picture: solutions have too-small particles to form a dispersed phase, and suspensions have particles that are too large and tend to settle; nonelectrolyte concerns conductivity rather than particle size.