Linear magnification produced by a concave mirror may be
A. Equal to $1$
B. Less than $1$
C. More than $1$
D. All of the above

Hint: When the object’s image is formed after the reflection in the mirror, the image size changes from the object size depending upon the position of the object that is in front of the mirror. The laws of the reflection of the mirror are used to find the change in size.

Complete step by step solution:
The linear magnification refers to the ratio of the size of the image to the size of the object. The negative value of the linear magnification refers to the image formed as inverted.
We can write the linear magnification as,
$ \Rightarrow m = \dfrac{{h'}}{h}$
Where,
$h'$ is the size of the image, $h$ is the size of the object.
The concave mirror produces the linear magnification based upon the image of the object that is formed. When the object that is placed between focal length and the center of the curvature, the image formed will be smaller than the object. When the object is placed at the center of the curvature the image that is formed is equal to the object. When the object is placed beyond the center of the curvature the image is formed beyond the center of the curvature.
Therefore, the concave mirror produces the linear magnification that may be more than $1$, or may be less than $1$, or equal to $1$, because it can form images that are smaller than the object.
Hence, the correct answer is option $\left( d \right)$.

Note:
Linear magnification can also be called lateral or transverse magnification. Linear magnification is always perpendicular to the optical axis. The longitudinal magnification can be denoted when the image increases in size when measured along the optical axis.