The image of a mountain can be seen on the surface of calm water. what property of light is demonstrated?

It is Reflection of light from water surface

Explanation:

When light coming from the mountains incident on the stationary water surface then major proportion of light gets reflected from the surface of water and this will received by the observer eye.

We also know that when light beam gets reflected into the form of beam then it is known as regular reflection.

Here when water surface is calm then the surface is assumed to be plane and in this case the light gets reflected by the surface of water in same direction and we got a good image in the water.

So this property of image is due to reflection of light.

3. dark matter

empty space could also be a simple vacuum