What type of backflow prevention device is commonly used for hose bibs?

The correct choice is a vacuum breaker, as this device is specifically designed to prevent backflow at points such as hose bibs, where a hose may be connected. A vacuum breaker works by allowing air to enter the system to prevent siphoning when there is a drop in water pressure. This mechanism is crucial for ensuring that contaminants cannot be drawn back into the potable water supply when the pressure fluctuates.

Other options, while they serve important roles in backflow prevention, are not typically used for hose bibs. A check valve can prevent backflow but does not provide air relief, which is necessary for situations where a hose could create a siphon. An air gap is a physical separation between a water supply and a potential contaminant, but it isn't practical for connections like hose bibs. Meanwhile, a reduced pressure zone device is more complex and used in situations where there is a higher risk of backflow contamination, usually in commercial plumbing systems, making it unnecessary for simple hose bib applications. Thus, the vacuum breaker is the most suitable and effective choice for hose bib protection against backflow.