Final answer:
A wetting agent, also known as a levigating agent, is a substance that reduces the surface tension of a liquid, aiding in its spreading on surfaces. Surfactants like soaps and detergents are examples of wetting agents that allow water to better wet surfaces by disrupting intermolecular interactions.
Step-by-step explanation:
A wetting agent, or levigating agent, is a type of substance that helps spread a liquid on a solid by reducing the surface tension of the liquid. The correct answer to what a wetting agent is would be 'a) Substance that reduces the surface tension of a liquid, aiding in spreading'. Surfactants, such as soaps and detergents, are typical examples of wetting agents, as they disrupt the intermolecular interactions between molecules of a polar liquid like water, making the water better able to wet surfaces.
These agents are essential in various applications, including in soaps, which can create emulsions to help lift dirt and grease by loosening their grip and allowing water to spread over them. This concept is based on the idea of adhesion, where the tendency of a liquid to spread on or interact with another substance can overcome the cohesive forces within the liquid itself. It's important to note that wetting agents do not act as thickeners or emulsion stabilizers, nor do they prevent settling in a suspension.