Question

Oxygen in expired air
A. 10%
B. 16%
C. 19%
D. 4%

Answer 1

Hint: In this question we will have a look at the process of respiration and try to study the process to know why will there be any oxygen present in the exhaled or expired air and then we will answer as to what is the amount of oxygen in the air exhaled by humans.

Complete answer:
The process of respiration is necessary for human existence. Through this process our bodies acquire oxygen and discard the carbon dioxide from our bodies. This oxygen is used in a chemical reaction inside our body which produces the ATP (Adenosine Triphosphate) form food we intake.
During the process of respiration all the oxygen in air inhaled does not get absorbed by our lungs. Only a small quantity is absorbed. So, there is some amount of oxygen in exhaled or expired air. This happens because the transfer of oxygen from the air sacs in lungs to our blood vessels takes place due to the process of diffusion. The difference in the concentration between the two is the driving force for this process, so when the driving force is not enough, the process stops and no more oxygen from air is taken. And then the air is exhaled with the remaining oxygen. The air we intake has about 21% of oxygen and the exhaled air has about 16% of oxygen.

So, the correct answer is “Option B”.

Note:
One can make a mistake of considering that all the oxygen from air must be absorbed or a major position of the oxygen present in air must be absorbed by the body. But as you can see that is wrong and only a small portion of oxygen in air is absorbed by the body.