In which of the following conditions the respiratory muscles are relaxed

(Functional residual capacity) (652- Ganong 22th) (621- K.S. 4th) (444- A.K.Jain 3rd) (593- Ganong 23rd)The lung volume at which airway pressure is 'zero' mm Hg is called relaxation volume, whch is equal to FRC.Therefore, relaxation volume is the point where the recoil of the chest and the recoil of the lungs balanceResidual volume - The amount of air remaining in the lung even after forced expiration(i) It helps to aerate the blood in between breathing and during expiration(ii) It maintains the contour of the lungs