Object is placed between infinity and a device. Image formed is diminished and between pole and focus, behind it. If the image is virtual and erect, identify the device.
A) Convex mirror
B) Concave mirror
C) Spherical mirror
D) Plane mirror

Hint:Recall the concept of curved mirrors. The curved mirrors are the mirrors that have a reflecting surface. The curved mirrors have a surface of the shape of a sphere. A spherical mirror is of the shape that is cut out of a spherical surface.

Step-By-Step Explanation:
Step I:
A surface that forms a clear image after reflection is known as mirror. A concave mirror is a mirror that has its curved surface towards the inner side. A concave mirror is also known as a converging mirror. This mirror can not form an erect image when the object is placed behind the mirror.
Step II:
Also when the object is placed behind the mirror, then the image formed will be erect but not diminished in size. If the image formed by the mirror is erect and virtual, and the object is placed between infinity and a device.
Step III:
Therefore, the device is a convex mirror.
$ \Rightarrow $Option A is the right answer.

Note:It is to be noted that the concave mirror has some similarities with convex lenses. The convex lens is also known as a converging lens because it also converges all the light rays parallel to the principal axis at a single point. Also the focal length of both concave mirror and the convex lens is positive. Also the nature of image formed by a convex lens and concave mirror is similar. The convex lens and concave mirror form a virtual, erect and magnified image when the object is placed between pole and the focus.