Answer
Plane
There are two types of curved mirrors, concave and convex. Both curved mirrors form that are magnified.
Concave will form an image on the same side as the object and it may not be the mirror used.
Plane mirror on the other hand forms images behind the mirror in all cases. The image formed is upright meaning it is virtual.
∴ The mirror used is a plane mirror.
Copper, gold and silver are three of them.
