<prompt> Shifting dullness is the characteristic sign ofHydropneumothoraxPneumothoraxConsolidationCollapse  <response>: Hydropneumothorax is collection of both fluidlower pa and airupper pa in the pleural cavity.The hallmark diagnosis in hydropneumothorax is 3 S:Shifting dullnessdue to the presence of free fluid air within the pleural cavity,dullness of fluid shifts from one place to other within chest with the change of posture of the patient,Succussion splash,and Straight fluid levelupper limit of dullness is horizontal. 