Final answer:
An air break provides a physical separation in plumbing systems to prevent backflow contamination into the potable water supply, serving as a simple but effective backflow prevention device.
Step-by-step explanation:
An air break provides a physical separation between the fixture indirect waste pipe and the reception. The correct answer to the question is d: air break. An air break is used in plumbing to prevent contaminated water or backflow from entering the potable water supply. It creates a gap between the fixture and the point of discharge which acts as a simple but effective backflow prevention device. It is critical in situations where a fixture's waste line is connected to a drain that could potentially allow for back-siphonage or back pressure of sewage into a fixture that is below the flood rim level.