The question that would best be answered by an experiment is: Question #1: Does reducing screen exposure two hours before bedtime decrease the time it takes to fall asleep?
This question is experimental in nature because it involves manipulating a variable (screen exposure) to observe the effect on another variable (time to fall asleep). An experiment would allow for a controlled comparison between individuals with reduced screen time versus those who do not reduce screen time before bed.
In contrast, Questions #2 and #3 are observational in nature. Question #2 compares groups based on age without manipulation, and Question #3 measures an average without an experimental treatment.