Which statement is true regarding rescue breaths for adults?

The statement regarding rescue breaths for adults being that each breath should last about 1 second is correct because the goal of delivering a rescue breath is to ensure that the air reaches the victim's lungs effectively while avoiding over-inflation. Each breath given should be delivered over approximately 1 second to allow for proper inflation of the lungs without causing damage. This timing helps to mimic natural breathing patterns, making it more effective and safer for the individual receiving assistance.

The other options, while they may seem reasonable at first glance, do not align with recommended practices for administering rescue breaths. The guideline of delivering one breath every five seconds might not allow for timely oxygenation in an emergency, as it is essential to provide ventilation more frequently. Continuously giving breaths without stopping is impractical, as intervals are necessary for monitoring the victim's response. Finally, leaving the mouth slightly open between breaths is not advised because a proper seal is important to ensure that the air is delivered effectively into the lungs, maintaining the efficiency of the rescue breaths.