Question

why can we not see the moon on a new moon night

Answer 1

on that day the light reflected part of the moon is not visible

Answer 2

   We only see the Moon because sunlight reflects back to us from its surface. During the course of a month, the Moon circles once around the Earth. If we could magically look down on our solar system, we would see that the half of the Moon facing the Sun is always lit. But the lit side does not always face the Earth!