Which statement best describes chemical properties of matter? chemical properties, such as density, must be observed when a substance is in its natural state at room temperature and normal atmospheric pressure. chemical properties, such as reactivity, must be observed when a substance is in its natural state at room temperature and normal atmospheric pressure. chemical properties, such as combustibility, are generally observed as the identity of a substance changes and one or more new substances form. chemical properties, such as boiling point, are generally observed as the identity of a substance changes and one or more new substances form.

Chemical change involves formation of new substances. Hence, the correct answer is "Chemical properties, such as combustibility, are generally observed as the identity of a substance changes and one or more new substances form."

The principal thing about a chemical change is that the identity of the substance must change. The identity of the substance must change as bonds between atoms of the substance are broken and rearranged.

Combustibility is a chemical property. It is observed as a substance is transformed into its oxide giving out heat and light in the process.

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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.

answersilicon (si); oxygen (o);