A small object is placed $10\text{cm}$ in front of a plane mirror. If you stand behind the object $30\text{cm}$ from the mirror and look at its image, the distance between the observer and the image of the object will be

The correct option is C $40\text{cm}$

For plane mirror,
Object distance = image distance$=10\text{cm}$
Distance between observer and mirror $=30\text{cm}$
The distance to be focussed by observer in order to see the image is,
$=30+10=40\text{cm}$
Hence, option $\left(c\right)$ is the correct answer.