Which of the following is a chemical change A melting ice B boiling water C a burning candle or D Frost forming inside of freezer

Burning candle is a chemical change.

Option C

Explanation:

Chemical change is an irreversible change both in composition and phase. It involves breaking of bonds completely. So among the given options, the melting ice, boiling water and frost forming are reversible changes.

All these three occur by increasing the temperature and the composition will remain constant even after melting of ice, boiling of water and frost forming. But the candle once burned will not be able to come to the same position again.

So, the burning of candle will lead to formation of melted wax, which cannot be again made to candle. So the process of burning of candle is the chemical change as there will be change in the composition after the candle was burnt.

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.