What is adsorption, and which pollutant is commonly removed by adsorption on activated carbon?

• A. Adsorption is when pollutants dissolve into a liquid; activated carbon removes salts from water.
• B. Adsorption is when pollutants are chemically altered by sunlight; activated carbon neutralizes odors.
• C. Adsorption is when molecules attach to a surface; activated carbon adsorbs many organics and odors from water.
• D. Adsorption is when pollutants rise to the surface and evaporate; activated carbon vaporizes contaminants.

Answer: (C)

Adsorption is a surface attachment process where molecules stick to the surface of a solid rather than dissolving into the liquid. Activated carbon has a very large surface area because of its numerous tiny pores, so it can attract and hold organic molecules and odorous compounds on its surface. That makes it effective for removing many organics and odors from water. The other descriptions describe different processes—dissolution into water, photochemical changes, or evaporation—and salts aren’t mainly removed by adsorption on activated carbon.