The size of ions as measured by ionic radii varies in a systematic manner. the size of the ion can be explained in part by effective nuclear charge, zeff, which is the net nuclear charge felt by an electron. the effective nuclear charge takes into account the actual nuclear charge and the shielding of this charge by inner electrons. when an atom loses electrons, the resulting cation is smaller both because the remaining electrons experience a larger zeff and because these electrons are usually in orbitals closer to the nucleus than the electrons that were lost. the more electrons that are lost, the smaller the ion becomepart arank the following ions in order of decreasing radius: rb+,k+,li+,cs+, and na+.rank from largest to smallest radius. to rank items as equivalent, overlap them. part brank the following items in order of decreasing radius: ca, ca2+, and ca2−.rank from largest to smallest radius. to rank items as equivalent, overlap them. part cthe following ions contain the same number of electrons. rank them in order of decreasing ionic radii. cl^- ; ca^2+ ; s^2- ; k+ ; p^3-; sc^3+rank from largest to smallest radius. to rank items as equivalent, overlap them.

1:Decreasing atomic radii

C's+,Rb+,K+,Na+,andLi+

2:decreasing atomic radii

C2-,Ca&C2+

3:from largest

Sc3+,Cl-,S2-,P3-,K+&Ca2+

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.