Which contaminants are removed by adsorption?

Adsorption is a process in which contaminants adhere to the surface of a solid material, often referred to as an adsorbent. This technique is particularly effective for removing a variety of organic and inorganic substances from water due to the adsorbent's ability to attract and hold certain molecules based on their chemical properties.

The correct answer identifies contaminants such as cyanide, PCBs (polychlorinated biphenyls), pesticides, phenols, and solvents, all of which can be effectively removed through adsorption. These substances are often hydrophobic (water-repellent) or have specific functional groups that allow them to bind strongly to adsorbent materials like activated carbon. Adsorbents are especially valuable in treating hazardous waste and purifying drinking water, as they can significantly reduce the concentration of these harmful contaminants and protect human health and the environment.

In contrast, the other options either involve contaminants that are not typically addressed through adsorption or contaminants that are more effectively removed through different methods such as filtration or chemical precipitation. For example, heavy metals are more commonly removed through processes such as precipitation or ion exchange, while microorganisms may require disinfection methods rather than adsorption.