Why is mercury coated on the back of the mirror?
Answer: Mirror is made of glass. Glass is a transparent material. As a result, when light falls on the glass, most of the incident light rays are refracted through the glass and go to the other side. A very small amount of light is reflected. Mirrors are therefore made by coating them with opaque mercury so that most of the light rays are reflected by the opaque coating and reflections are formed in the mirror.