Sodium (na) has 11 protons and 12 neutrons. which of the following is the most likely atomic weight of sodium?
22.98
12.98
11.98
24.98

22.98 is the most likely atomic weight of sodium

Explanation:

Sodium is a mono-isotopic element and its atomic weight is determined solely by its isotope.Usually Atomic masses are not integers since they are taken as the average weight of  the atomic mass of the  isotope of the element that are occuring  naturally. atomic weight of the atom depends on the 'atomic mass unit' (amu), that  is 1/12th of  the mass of carbon-12 present in its ground state.  Electrons  also contribute to the atomic mass.

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.

answers: to make sure that all of the broken pieces of tablet were added to the water, to allow for fair comparison of all three trials, with different particle sizes to avoid experimental error