Acompound is found to contain 23.3% magnesium, 30.7% sulfur and 46.0% oxygen. what is the empirical formula of this compound?

MgSO_3

As is standard for these sorts of questions, we assume 100 g of substance, and use the percentage elemental compositions to calculate an empirical formula.

"Magnesium" = (23.3*g)/(24.31*g*mol^-1) = 0.958*mol

"Sulfur" = (30.7*g)/(32.06*g*mol^-1) = 0.958*mol

"Oxygen" = (46.0*g)/(15.999*g*mol^-1) = 2.86*mol

We divide thru by the smallest molar quantity (0.958*mol) to get and empirical formula of MgSO_3, magnesium sulfite.

Ordinarily you would not be given the percentage of oxygen by mass. You would be given the percentages of the metal and sulfur, and would have to assume that the balance was oxygen.

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.