When you forcefully exhale your entire expiratory reserve volume, any air remaining in your lungs is called the residual volume (rv). why is it impossible to further exhale the rv (that is, where is this air volume trapped, and why is it trapped).

Keeping the alveoli open and for constant gas exchange.

Explanation:

After maximum expiration of the air in the lungs, there remains still some air called the residual volume. This is because the alveoli, the smallest sacs in the lungs which take part in the exchange of gases between the lungs and the bloodstream, need to stay inflated and open. This also ensures that the gas exchange is continuous between breaths which is really important. I hope this answer helps.