Which of the following elements has the lowest ionization energy? Na

C

F

He

Rb

Rb

Explanation:

Ionization energy is defined required energy to eliminate or remove an electron from an ion or atom.

From the given elements Rb or Rubidium has the lowest ionization energy as it has lowest shielding effect, so it easy to remove electron from it's shell.

The ionization energy generally decreases from top to bottom in groups due to lower shielding effect and outer electrons are loosely packed so easy to remove and increases from left to right across a period because of valence shell stability.

Rubidium has atomic number 37 and lies below than other given elements and also placed in the left side in the periodic table.

Hence, the correct option is Rb

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.

the correct answer is:

a. formation of precipitation