Is carbon dioxide a pure substance

Yes, carbon dioxide is a pure substance not a mixture. First consider the properties of a pure substance: •made of only one type of atom or molecule

Explanation:

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Explanation:

A pure substance needs only be made up of only one kind of molecule or it could be an ionic or metallic solid made up only of the atoms in the empirical formula, not necessarily one kind of atom. It is possible to have pure carbon dioxide, pure water, pure oxygen gas pure NaCl solid and pure solid iron, in theory only. It’s literally impossible to ensure that every single atom or molecule of ‘something else’ is removed from anything.

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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.