Choose the correct option to complete the statements given.
Full moon night occurs once every______.
A) Day
B) 15 days
C) 20 days
D) Month

Hint:Moon is the only natural satellite of our planet Earth. It revolves around Earth every day. Full moon is a condition where the moon appears to be fully illuminated. We need to choose whether this condition appears every day, 15 days, 20 days or every month. Then with that we will be able to fill the gap and complete the sentence given to us.

Complete step by step answer:
The lunar phase in which the Moon appears fully illuminated from Earth's viewpoint is called full moon. This situation occurs when Earth is located between the Moon and the Sun. In this the lunar hemisphere facing Earth, i.e,the near side is completely sunlit and appears to be as a circular disk. The time interval between a full moon and the next repetition of the same phase, i.e., a synodic month, averages about 29.53 days.So, the full moon roughly appears once a month.

Thus, option (D) Month, is correct. So, “Full moon night occurs once every month.”

Note: At Full Moon, the Moon is opposite to the Sun, i.e., 180 degrees away, and 12 hours behind it. So, the exact opposite thing happens as the Moon rises as the Sun sets. At midnight, it's high in the south, and it sets in the morning, when the sun rises.