The mirror used by a dentist to examine the teeth of patients is

The correct answer is A, concave.

A dentist needs a magnified, upright image of a small tooth surface, and a concave mirror gives exactly that when the tooth is placed inside its focal length. The mirror forms a virtual, erect and enlarged image, so the surface looks bigger and the dentist can see detail clearly. The same principle is used in shaving mirrors and in the head mirrors used by ENT and eye specialists.

Why the others fail:

• Convex (B): always gives a diminished image. It suits vehicle rear-view mirrors because it gives a wide field of view, which is the opposite of what a dentist needs.
• Plane (C): gives an image of the same size, so there is no magnification.
• Cylindrical (D): curves along one axis only, so it distorts the image in one direction and is not used for magnified inspection.

Core concept: the mirror formula 1/v + 1/u = 1/f and the magnification m = v/u, which is positive for a virtual erect image. This is the basis of many medical instruments and a useful link to Science and Technology in Mains.

Trap: candidates pick convex because it is the familiar mirror in vehicles, or pick plane because the dental mirror looks flat at first glance. Ask what the job requires: magnification means concave.