Microbiology When the respiratory muscles are relaxed, the lungs are in which of the following state? A Functional residual capacity (FRC) B Expiratory reserve volume (ERV) C Residual volume (RV) D Inspiratory reserve volume (IRV) 💡 Explanation When the respiratory muscles are relaxed, the lungs are in which of the following state? ✓ Correct Answer: A. Functional residual capacity (FRC)