What types of mirrors are used in ATM counters?
(A) Concave
(B) Convex
(C) Plane
(D) None

Hint: To answer this question, we have to analyse the properties of each of the mirrors given in the question and relate them with the requirement of a mirror in an ATM counter. The one with the properties fulfilling this requirement will be the correct choice.

Complete step-by-step answer
In ATM counters, the mirror is provided to let the customer know what is there in the background of him, while he is entering the password and withdrawing the cash. This is done to make the customer aware of any suspicious behaviour going in the background.
For this requirement, the mirror needs to form the image of a much wider amount of the area of the background.
In the case of a plane mirror, the image formed is equal in size as that of the object. So, it cannot cover a wide area of the background. For covering this wide area, a plane mirror having equally wide surface area is required, which is not practically possible.
So, option C is incorrect.
In the case of a concave mirror, the image formed is always magnified. So, it will cover only a small portion of the background, just doing the opposite job to that required.
So, option A is also incorrect.
Now, in the case of a convex mirror, the image formed is always diminished. So, it will form diminished images of each object present in the background, covering a much wider area. So, it is able to fulfil the requirement.

Hence, the correct answer is option B, convex.

Note: Due to their ability to form diminished images and hence covering a wide area, convex mirrors are very popularly used in the vehicles and the automobiles as the rear view mirrors. The convex mirror diverges the rays of light falling on its surface. So, it is also used in sunglasses, which protect our eyes from the harmful radiations coming from the sun.