What is the magnification produced by the plane mirror?

The correct option is "+1".

Step-by-Step Explanation:

Linear magnification ($m$) for a mirror is defined as the ratio of the height of the image ($h_i$) to the height of the object ($h_o$):

$$m=\frac{h_i}{h_o}$$

For a plane mirror, the image formed has two key characteristics:
1. Equal Size: The size of the image is always equal to the size of the object. Therefore, the magnitude of the image height is equal to the object height:
$\left|h_i\right|=\left|h_o\right|$
2. Erect Image: The image formed is virtual and erect (upright). According to the Cartesian sign convention, the height of an erect image is taken as positive, just like the object height.

Since both heights are positive and equal in magnitude, we have:
$h_i=h_o$
Substituting this relation back into the magnification formula:
$$m=\frac{h_o}{h_o}=+1$$

In this result, the plus sign ($+$) indicates that the image is virtual and erect, while the numerical value $1$ confirms that the image is of the exact same size as the object. Thus, the magnification produced by a plane mirror is always $+1$.