An isothermal plug flow reactor is used to remove an environmental contaminant from polluted water via a 2nd-order reaction. a residence time of 7.5 min in the reactor results in 90% conversion. to obtain 99% conversion, what is the closest time below that would be expected? explain your answer. a. 8.2 min b. 15 min c. 80 min d. 250 min e. 1500 min