<prompt> Critical Closing volume isVolume at the end of forceful expirationVolume at the end of forceful inspirationVolume remaining after Functional Residual Capacity is measuredClose to Residual Volume  <response>: Ans is d i.e. Close to Residual Volume Ref: Physiologic Basis of Respiratory Disease by Qutayba Hamid, Joanne Shannon, James Martin pi37; Surgical Critical Care and Emergency Surgery: Clinical Questions and Answers By Forrest O. Moorep7; closing volume is the minimum volume and pressure of gas necessary to prevent small airway collapse. It is somewhat near Residual volume.Under pathological conditions when CCV exceeds Functional Residual Capacity FRC, alveolar collapse occurs.FRC is Residual volume Expiratory reserve volume 