Answer:
During the full moon phase, the entire illuminated portion of the moon is visible from Earth. This occurs when the Earth comes between the sun and the moon. We see a bright disc of the moon.
On the other hand, during new moon phase, the entire illuminated portion of the moon faces away from the earth and we don't see the lit face of the moon. This happens when the moon comes between the Sun and the Earth. Viewing a new moon is very difficult as the moon appears very dark.