A fuel oil is fed to a furnace and burned with 35.0% excess air. The oil contains 86.0 wt% C, 10.0% H, and 4.00% S. Analysis of the furnace exhaust gas shows only N2, O2, CO2, SO2, and H2O. The sulfur dioxide emission rate is to be controlled by passing the exhaust gas through a scrubber in which most of the SO2 is absorbed in an alkaline solution. The gases leaving the scrubber (all of the N2, O2, and CO2, and some of the H2O and SO2 entering the unit) pass out to a stack. The scrubber has a limited capacity, however, so that a fraction of the furnace exhaust gas must be bypassed directly to the stack.

At one point during the operation of the process, the scrubber removes 90% of the SO2 in the gas fed to it, and the combined stack gas contains 612.5 ppm (parts per million) SO2 on a dry basis; that is, every million moles of dry stack gas contains 612.5 moles of SO2. Calculate the fraction of the exhaust bypassing the scrubber at this moment.

1. the question asks the most appropriate, which seems to rule out "all of the above." your choice appears to be the correct one.

2. the protocol described is good for identifying correlation, but not cause and effect. for cause/effect, you need to devise a protocol that will assign the treatment (or not) to groups that have essentially the same "demographics" with respect to all the other variables. your choice regarding control group seems appropriate. random assignment of treatment (choice d) may be appropriate also. (i think you can argue that b and d are just different descriptions of the same method.)

3. d will randomize the birds, but may not guarantee there are 10 in each group. e will do both, so seems the better choice.

comment on question 2

based on the problem statement, it seems clear that confident, attentive drivers are more likely to use daytime running lights. so, the protocol might need to be devised in such a way that the lights would be turned on or off without the driver's knowledge. (an attentive driver will figure it out.) assigning a confident, attentive driver to a group required to drive without running lights might mess with his/her confidence and attentiveness. you don't want your experiment to do that. (nor do you want the experiment to subject a driver to greater risk of accident as a consequence of driving without running lights.) experiments involving human safety are always problematic.