To get an image of same size the object should be placed at the center of the curvature of a concave mirror.
Given,
focal length = 25 cm
As, centre of curvature = 2 x focal length
Therefore,
centre of curvature
= 2 x 25
= 50 cm
Hence, the object should be kept at 50 cm so that the size of image is equal to the size of object.