Adsorption is an unit operation which generally involves __________ systems.

ANS:C - fluid-solid

"Fluid-solid" refers to a system where a fluid interacts with a solid material. This interaction can occur in various contexts and processes across different industries. Here's an explanation:

1. Fluid-Solid Interaction in Fluid Mechanics: In fluid mechanics, fluid-solid interaction refers to the behavior of a fluid (liquid or gas) as it flows past or interacts with a solid surface. This interaction can lead to phenomena such as fluid flow around objects (aerodynamics), boundary layer formation, drag forces, and heat transfer between the fluid and solid surfaces.
2. Fluid-Solid Contact in Unit Operations: In the context of unit operations in chemical engineering, fluid-solid interaction occurs in processes where a fluid contacts or interacts with a solid material for separation, purification, or transformation purposes. Examples of unit operations involving fluid-solid interaction include:
   • Filtration: Where a fluid (liquid or gas) passes through a porous solid medium, such as a filter or membrane, allowing for the separation of suspended particles or contaminants from the fluid.
   • Adsorption: Where a fluid (gas or liquid) adheres to the surface of a solid material (adsorbent) through physical or chemical interactions, leading to the removal or separation of specific components from the fluid stream.
   • Absorption: Where a gas or liquid is absorbed into a porous solid material, often for the purpose of capturing or removing certain components from the fluid phase.
   • Catalysis: Where a fluid reacts with a solid catalyst surface, leading to chemical transformations or reactions within the fluid phase.
3. Applications: Fluid-solid interaction is encountered in various industries and applications, including chemical processing, wastewater treatment, environmental remediation, pharmaceutical manufacturing, and materials processing. Understanding and controlling fluid-solid interaction is crucial for optimizing the performance and efficiency of these processes.