Question

Where an object should be placed in front of a concave mirror so as to get unit magnification

Answer 1

the mirror should be placed at radius of curvature of the lens as magnification=1 which means image distance and object distance should be same and the height of image and height of object should be same which is only possible in the case of object placed at radius of curvature(or 2f)

hope this helps!

Answer 2

It should be placed at a centre of curvature to get unit magnification . An object should be placed at the centre of curvature for an image to form the light while coming for infinity will  an image in front of the concave mirror.