Why does exchange of gases continue to occur in the lungs even if you hold the breath for 30 second

Why does exchange of gases continue to occur in the lungs even if you

1.	Why does exchange of gases continue to occur in the lungs even if you hold the breath for 30 second
Answer» Due to presence of RESIDUAL volume of air in the lungs. It ensures continuous exchange of respiratory gases in the alveolar sacs even when we forcefully exhale air or hold our breath for a few seconds.