Question

why the temperature of moon falls to-190°C?

Answer 1

cause there is no atmosphere to maintain balance of temperature

Answer 2

There is nothing to hold the heat in the soil and rocks that compose the surface, so the surface is exposed to the temperature of empty space, which is extremely cold. The side of the moon facing the sun is broiling hot also because there is no atmosphere ... nothing to reflect any portion of the sun's energy before it reaches the surface.