State the volume of air remaining in the lungs after a normal breathing.

(N/A) The volume of air remaining in the lungs after a normal expiration is known as functional residual capacity $(FRC)$.
It includes expiratory reserve volume $(ERV)$ and residual volume $(RV)$.
$ERV$ is the additional volume of air that can be exhaled after a normal expiration,which is about $1000 \, mL$ to $1100 \, mL$.
$RV$ is the volume of air remaining in the lungs even after a forced expiration,which is about $1100 \, mL$ to $1200 \, mL$.
Therefore,$FRC = ERV + RV$.
$FRC \approx 1000 \, mL + 1100 \, mL = 2100 \, mL$ to $1100 \, mL + 1200 \, mL = 2300 \, mL$.
Thus,the functional residual capacity of the human lungs is approximately $2100 \, mL$ to $2300 \, mL$.