When taking pH measurements of solutions, why is it important to stir thoroughly after adding each reagent? a. Mixing helps keep the solution components from contaminating the pH meter. b. A pH meter can only measure ions that are flowing past the meter at a fast speed. c. Mixing helps prevent precipitation of insoluble salts out of solution. d. Mixing helps ensure that the heasured pH is reflective of the entire solution.

d. Mixing helps ensure that the measured pH is reflective of the entire solution.

Explanation:

Hello there!

In this case, according to the given information, it turns out possible for us to reason that the answer is d. Mixing helps ensure that the measured pH is reflective of the entire solution because mixing help us to move the ions all around the solution so it undergoes homogenization and the measured pH at any point of the solution will be the same.

Moreover, we need to keep in mind that the incomplete stirring leads to regions with more concentration of the acid or base, or what we know as a gradient of concentration, which may lead to a incorrect measurement.

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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.

all eukaryotic cell have mitochondria : )