When the respiratory muscles are relaxed, the lungs are at which of the following?

The functional residual capacity (FRC) occurs at the lung volume at which the outward recoil of the chest wall is equal to the inward recoil of the lungs,which occurs when no respiratory muscles are actively contracting, that is,at the end of a tidal expiration. The FRC is therefore also referred to as the resting expiratory level, or simply, the resting level.