Is it possible for a lens to act as a convergent lens in one medium and a divergent lens in another?

An object is placed at a distance of $12 \ cm$ in front of a concave mirror. It forms a real image four times larger than the object. Calculate the distance of the image from the mirror. (in $cm$)

The image of a candle flame formed by a lens is obtained on a screen placed on the other side of the lens. If the image is three times the size of the flame and the distance between the lens and the image is $80 \, cm$,at what distance should the candle be placed from the lens? What is the nature of the image at a distance of $80 \, cm$ from the lens (in $, cm$)?

Discuss the position and nature of the image formed by a concave mirror when the object is moved from infinity towards the pole of the mirror.

What type of image is formed by a plane mirror?

The diagram given below shows an object $O$ and its image $I.$ Copy the diagram and draw suitable rays to locate the lens and its focus. Name the type of lens in this case.