What is characterized by pore spaces being completely filled with water?

The correct answer is characterized by the situation where all the pore spaces within the soil or rock are fully filled with water, leading to the formation of the saturated zone. In the saturated zone, water occupies all available voids, resulting in a pressure head and allowing for the movement of groundwater. This zone is typically found beneath the water table, which separates it from the unsaturated zone above, where some pore spaces contain air and are not fully saturated with water.

The concept of the saturated zone is crucial in understanding groundwater aquifers and how water is stored and transferred in geological formations. In contrast, the unsaturated zone above contains varying amounts of water and air, making it not fully filled, while the water table marks the boundary between these two zones, rather than describing the characteristics of the pore spaces themselves. The term "pore space" refers more generally to the voids in any material, without specifying their contents, which can include air or water depending on the context.