What is the function of the layer of metal behind glass of a mirror

i would like to tell u that there is no metal behind a mirror
no there is then how can others can tell answer of my question tell me uncle
Uncle Jo ke bete mirror ke peche silver paint air use upar White or black paint Kia kata hai


Tomake that surface opaque and the other surface reflecting and thus we can make it as amirror
usally its coated with mercury which is a liquid metal
to prevent mirror from becoming transpetent substance as one could see image. it was the function of metal which was coated on one side of the mirror.