At certain times during each month, the moon is entirely invisible from earth, even on a clear night. which phase of the moon is this?
a) full moon.
b) first quarter moon.
c) new moon.
d) third quarter moon.

C) New Moon

Explanation:

The Moon has several phases. The phases are a result of the position of the Moon, Earth, and Sun relative to each other. The Moon is not an object that produces light, but instead it reflects the light from the Sun, so it can be seen from Earth as a bright, or partially bright object in the sky, except for one day in the month when it can not be seen.

The phase in which the Moon can not be seen is called New Moon phase. The Moon is totally lacking from the sky, or rather it seems that way because it can not be seen with naked eye. The reason for this is that the Moon is located between the Sun and Earth, so the half that is lighted by the Sun is facing the Sun, while the opposite side that is facing the Earth is not lighted at all, so the Moon is dark on this side.