Answer: The answer is the number of hours of daylight each day.
Step-by-step explanation: We are to give the best example of a natural phenomenon of periodic behavior.
A periodic behavior means the behavior which repeats itself in equal intervals of time or periods. Since we are talking about a natural phenomenon, so the rotation of earth around the sun can be an example.
In other words, we can say the number of hours of daylight each day will be the proper example, because the sun gives light for almost same number of hours each day.
Thus, the natural phenomenon is the number of hours of daylight each day.