How many voids are present in double brick and hollow block foundation walls?

The correct answer indicates that there is one void present in double brick and hollow block foundation walls. This understanding stems from the design and construction principles of these walls.

In a double brick wall, two layers of bricks create a cavity or void between them, which can provide insulation and moisture control benefits. In the case of hollow block construction, each block typically contains one or more voids within its structure for similar reasons—enhancing the wall's overall thermal efficiency or reducing weight. Together, the void created by the configuration of the two materials results in a single effective void that serves functional purposes related to structural integrity and environmental control.

Considering the other options, they imply the presence of multiple voids, which would not accurately represent the typical structure and function of double brick and hollow block foundation walls. Therefore, recognizing that there is one principal void in these types of construction is essential for understanding how they are designed and how they function under various conditions.