An unknown paraffinic hydrocarbon is defined by the chemical formula CxH2x+2. The paraffin is burned with air, and there is no CO in the combustion products. (a) After drawing and labeling a flowchart, use a degree-of-freedom analysis to determine how many variables must be specified to determine the flow rates of all components entering and leaving the combustion unit. Express the fraction excess air as y and write elemental balances in terms of x, y, and the molar flow rate of CxH2x+2. (b) Calculate the molar composition of the combustion product gas in terms of x for each of the following three cases: (i) theoretical air supplied (y = 0), 100% conversion of the paraffin; (ii) 20% excess air (y = 0.2), 100% conversion of the paraffin; (iii) 20% excess air, 90% conversion of the paraffin. (c) Suppose x = 3 (i. e., the paraffin is propane). Assuming complete combustion of the hydrocarbon, what is the ratio of CO2 to H2O in the product gas? Use this result to suggest a method for determining the molecular formula of the paraffin.

the answer to your question is c.

if you read the house of usher you should know that the house was haunted

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.