Which of the following ranges of hemoglobin O2 saturation from systemic venous to systemic arterial blood represents a normal resting condition?

Ans. D. 75 to 98%In a normal resting condition, the blood leaving the lungs is 98% saturated with oxygen, and the blood returning to the lungs is 75% saturated with oxygen. With vigorous exercise, blood leaving the lungs is still 98% saturated, but blood returning is usually less than 75% saturated because more oxygen is unloaded from hemoglobin in exercising muscles.