If a chemist has 2.3 moles of arsenic that has a molar mass of 74.92g/mol, which would be the best way to find out how many atoms of arsenic are in the sample?

multiply 2.3 bu the molar mass of arsenic.

divide 2.3 by the molar mass of arsenic.

multiply 2.3 by avogadro's number.

divide 2.3 by avogadro's number.

              Multiply 2.3 by Avogadro's Number

                     As we know that 1 mole of any substance contains exactly 6.022 × 10²³ particles which is also called as Avogadro's Number. So in order to calculate the number of particles (Atoms) contained by 2.3 moles of Arsenic (As), we will use following relation,

           Moles  =  Number of Atoms ÷ 6.022 × 10²³ Atoms.mol⁻¹

Solving for Number of Molecules,

           Number of Atoms  =  Moles × 6.022 × 10²³ Atoms.mol⁻¹ **

(**This is your answer)

Putting values,

           Number of Atoms  =  2.3 mol × 6.022 × 10²³ Atoms.mol⁻¹

           Number of Atoms  =  1.38 × 10²⁴ Atoms

Hence,

           There are 1.38 × 10²⁴ Atoms present in 2.3 moles of Arsenic.

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.

i do not get it   at all