Which of the following best describes colloidal substances?

Colloidal substances are best described as particles that typically range from about 1.0 to 0.005 micron in diameter. These particles are larger than dissolved ions and molecules but smaller than most particles that can be seen with the naked eye. They remain suspended in a liquid rather than settling out quickly like larger particulate matter. This size range allows colloidal particles to exhibit unique properties such as the Tyndall effect, where light is scattered by the particles, making colloids distinguishable from true solutions in which solutes are completely dissolved.

The choice indicating large particles over 1 micron does not accurately capture the definition of colloidal substances, as these larger particles may not remain dispersed in a liquid as colloids do. Additionally, stating that colloidal substances are completely dissolved in water misrepresents their nature, as true solutions do not have particles that are visible or that retain their structure when mixed. Lastly, describing colloids as only organic materials is also inaccurate, as colloids can be composed of inorganic particles as well. Thus, the correct description focuses on the specific size range that defines colloids.