One electron(s) are added to an phosphorus atom. Enter the chemical symbol of the element.

S (sulphur)

Explanation:

In a neutral atom, the number of electrons and the number of protons in an element are equal. These numbers are called the ATOMIC NUMBER. That is, in a neutral atom;

proton no. = electron no. = Atomic no.

Hence, in this case where phosphorus atom has an electron number of 15. It means that there are 15 protons and 15 electrons in a phosphorus atom. If one electron is added to these electrons i.e. 15 +1, there will be 16 electrons in the atom, hence, this atom becomes SULPHUR element, which has 16 electrons in its atom, with chemical symbol S.

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.

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.