Final answer:
In the normal resting state of the human body, hemoglobin in mixed venous blood is nearly 75% saturated with oxygen, representing a state where oxygen has been released to the tissues but still maintains an oxygen reserve.
Step-by-step explanation:
At the normal resting partial pressure of oxygen (PO₂) of mixed venous blood, hemoglobin is not fully saturated. When hemoglobin travels to the tissues, the partial pressure of oxygen drops to about 26 mm Hg, causing oxygen to be released and thus forming reduced hemoglobin (HHb). Venous blood still contains some oxygen bound to hemoglobin, which can be used when tissues demand more oxygen. Considering the saturation levels indicated, hemoglobin in mixed venous blood is nearly 75% saturated, which aligns with option (c).
Hemoglobin's ability to bind oxygen decreases as it achieves higher levels of saturation, and this is represented in the saturation/dissociation curve for oxygen and hemoglobin. Therefore, at the normal resting state, hemoglobin in venous blood is not nearly 100% or 97% saturated due to oxygen being released to the tissues. It's also not as low as 50% or 25% saturated, because under normal conditions, there is still a significant amount of oxygen bound to hemoglobin in venous blood, providing an oxygen reserve.