Final answer:
The amount of air not available for gas exchange in the average 70-kg adult's tidal volume is 50 mL.
Step-by-step explanation:
Tidal volume is the amount of air inspired and expired during normal breathing. To find the amount of air that is not available for gas exchange, we need to subtract the tidal volume from the total lung capacity. The total lung capacity is the sum of the residual volume, expiratory reserve volume, tidal volume, and inspiratory reserve volume. Since the question only asks for the amount of air not available for gas exchange, we can ignore the residual volume and expiratory reserve volume. Therefore, the amount of air not available for gas exchange is the inspiratory reserve volume.
Based on the given information, the average tidal volume for the 70-kg adult is not provided. However, the options provided are given in milliliters (mL). The inspiratory reserve volume is usually around 3100 mL for an average adult. Therefore, the answer is D. 50 mL because it is the only option that is significantly smaller than the inspiratory reserve volume.