In which of the following, the image of an object placed at infinity will be highly diminished and point sized?
Concave mirror
The image of an object placed at infinity will be highly diminished and point sized in a concave mirror. The image formed in a convex mirror, when the object is at infinity, will not be at the focus and will have a finite size. The image formed in the plane mirror will be as far as the object is from the mirror, and will have the same size as the object.
Hence, only in a concave mirror, the image formed by an object at infinity be at the focus and point sized.