Objects present in the dark room are not visible. But when the light is switched on, everything present in the room becomes visible. Why does this happen?

We are able to see objects because the light which gets reflected from those objects reaches our eye. So if one were, to begin with no light source, then no light rays get reflected from objects and hence no light enters the eye. That is why we are not able to see anything in a dark room and see the objects present in the room once the light is switched on.