Which of the following represents adequate spontaneous ventilation in an adult?

Adequate spontaneous ventilation in an adult typically involves a tidal volume that is between 500 to 600 mL and a ventilatory rate that is around 12 to 20 breaths per minute. This range is considered optimal for effective gas exchange, allowing sufficient oxygen intake and carbon dioxide elimination.

The option you have selected has a tidal volume of 600 mL, which falls at the higher end of the standard range, combined with a ventilatory rate of 12 breaths per minute. This configuration supports effective ventilation while preventing respiratory fatigue and maintaining the body's demands for oxygen.

Maintaining a tidal volume in this range helps ensure that each breath brings in enough air to adequately perfuse the lungs and deliver oxygen to the blood. Additionally, a ventilatory rate of 12 is within normal limits, reflecting a balance that would not strain the respiratory system.

Other options may either present tidal volumes that are too low or ventilatory rates that are either too high or too low, thus compromising adequate ventilation for an adult.