Final answer:
The unsaturated zone has pore spaces filled predominantly with air, while the saturated zone has pore spaces filled with water, constituting groundwater. The identification of groundwater sources for drilling wells involves finding high porosity and permeability in continuous sandstone aquifers.
Step-by-step explanation:
The part of the subsurface where most of the pore spaces are filled with air is the unsaturated zone (A). The area of subsurface where the pore spaces are filled with water is called the saturated zone (B).
The unsaturated zone is where the soil and rock below the land surface have pore spaces that contain air and some water, which is not enough to fill all the voids. This zone lies above the water table. On the other hand, the saturated zone is located below the water table where all the pore spaces are completely filled with water.
Locating groundwater for use in wells typically involves identifying areas with high porosity and permeability, such as sandstone aquifers, because these characteristics allow for the storage and movement of substantial quantities of water, making it easier to extract.