No, light cannot pass through opaque objects

No, we can not see any object in a completely dark room.

We can see the objects around us with the help of light.

In case of a plane mirror, an image which cannot obtained on the screen is virtual image.

The pinhole images are inverted while the shadow is different from it.

Luminous objects are those objects which emit the light of their own e.g. the stars, the sun, burning candle, etc. While non-luminous objects are those objects which do not emit light of their own, e.g. Blackboard, moon, earth, etc.

As we know that the silvered glass surface is very smooth and shiny as well. So, this type of surface helps informing the clear image. So, silvering makes it shiny and this shiny surface in turn helps in reducing the absorption.

The two ways through which a transparent glass sheet can be converted into a translucent sheet are
(i) If one side of butter paper gets covered, then a transparent glass sheet turns into a translucent one.
(ii) By smearing a thin layer of oil.

The dark patch of light is known as a shadow which is formed when there is an opaque object in the path of light.
When an image is the reflection of light. By seeing image, we can identify the object but shadow can mislead you from actual object.

Some of the properties of light which can be stated as follows
(i) Light is a form of energy.
(ii) It travels in a straight line.
(iii) For an opaque object, light casts a shadow.

The shadow of the object cannot be caught if the screen and the object are very far from each other. This is the same case, the shadow of the football cannot be seen on the ground when it is kicked high in the air. This happens because if we take the object away and away from the screen, the image becomes smaller and smaller and a time comes when it disappears from the screen.

Sometimes, the shadow of the object (ball) may not be formed because of improper arrangement. It may be that the direction of the torchlight is not towards the screen. The shadow will be formed only if screen, torch and ball are in the same straight line (as shown in figure).

The image can be observed behind wall using a periscope with the help of plane mirror by reflection of light.

So, when rays of light coming from tree behind the wall fall on plane mirror (P₁), then after reflection, it goes to the plane mirror (P₂), which again reflects the light rays towards viewer. Therefore, we can see the tree which is behind wall.