In which of the following pa of the lung the ventilation/perfusion ratio is maximum?

The ratio of pulmonary ventilation to pulmonary blood flow for the whole lung at rest is about 0.8 (4.2 L/min ventilation divided by 5.5 L/min blood flow). However, relatively marked differences occur in this ventilation/perfusion ratio in various pas of the normal lung as a result of the effect of gravity. Ventilation, as well as perfusion in the upright position, declines in a linear fashion from the bases to the apices of the lungs. However, the ventilation/perfusion ratios are high in the upper poions of the lungs. When widespread, nonuniformity of ventilation and perfusion in the lungs can cause CO2 retention and lowers systemic aerial PO2. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 34. Introduction to Pulmonary Structure and Mechanics. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.