An object is placed 20 cm in front of the plane mirror. The mirror is moved 2 cm towards the object. The distance between the positions of the original and final images seen in the mirror is:

The correct option is B $4\text{cm}$
An object is placed 20 cm in front of the plane mirror, then the image formed is 20 cm behind the mirror.
If the mirror is moved 2 cm towards the object
The distance between the object and mirror $=20\text{cm}-2\text{cm}=18\text{cm}$
The distance between the image and mirror $=20\text{cm}-2\text{cm}=18\text{cm}$
Therefore, the total distance between the positions of the original and final image is
d = distance of the original image - distance of the final image
$\text{d = 40 - 36}$
$\text{d = 4 cm}$