What is absorption?

Absorption refers specifically to the process where one substance is taken up into the structure of another material, which often involves fluids or gases. In the context of water treatment, absorption involves the interaction between a liquid and a solid where the liquid permeates the solid material. For instance, in water treatment, certain contaminants can be absorbed by activated carbon, effectively removing them from the water.

The other options, while related to different concepts, do not accurately define absorption. Being engrossed in something pertains to mental focus rather than the physical process of absorption. The breakdown of particles in water is more aligned with chemical processes or decomposition rather than absorption itself. Lastly, filtration is a distinct method employed to remove particles from water, typically involving separation based on size rather than the absorption process where one substance integrates into another. Hence, option A accurately captures the essence of absorption in the context of water treatment and related processes.