We're told oxygen is the most common element in the Earth's solid crust. But how much oxygen is there? Let's compare to the amount of oxygen in the Earth's atmosphere, like this: The most common minerals in the Earth's crust are feldspars, and anorthite (CaAl2Si2O8) is a typical feldspar. Let's assume the entire crust is made of anorthite, with a density of 2.8 g/cm .
The radius of the Earth is 6371. km and let's say the trust is the upper 100 km of it.
Let's model the Earth's atmosphere as a layer on top of the Earth about 100 km thick with an average density of 0.99 g/m, and which is 23.1% oxygen by mass.
Use this information to calculate the ratio of the mass of oxygen in the Earth's atmosphere to the mass of oxygen in the Earth's crust. Round your answer to 2 significant digits X 5 ?

20 2

Explanation:

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b is the correct

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.