The half-life of isotope x is 3 days, how long will it take for one half of 10g sample to decay

Answer : It will take 3 days for one half of a 10g sample to decay.

Explanation :  

Half-life period : It is defined as the time taken for half life of the reaction to complete that is the time in which the concentration of a reactant is reduced to half of its original value.

As per given in the question,

The half-life of isotope X = 3 days

when the original amount of sample (10g) will be half then the half-life of sample is, 3 days.

Hence, it will take 3 days for one half of a 10g sample to decay.

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.