A vapor stream containing 3.0 mole percent benzene is scrubbed with wash oil in a packed absorber to reduce the benzene concentration in the gas to 0.02 percent. The oil has an average molecular weight of about 250 and a density of 54.6 lb/ft² and contains 0.015 percent benzene. The gas flow is 1.500 ft³/min at 25°C and 1 atm. 

(a) If the scrubber operates isothermally at 25°C with a liquid rate of 14,000 lb/h, how many transfer units are required? 

(b) If the scrubber operates adiabatically, how many transfer units are needed? 

(c) What would be the major effect of operating with an oil of lower molecular weight, say, M = 200?