When a beam of light is incident on a plane mirror, it is found that a real image is formed. The incident light beam must be

The correct option is A Converging
In the case of a plane mirror if the object is real then reflected rays diverge from the mirror after reflection. Hence, a virtual image is formed.
For a real image, reflected rays must converge at a point after reflection. This is only achievable in the case of a virtual object.


Here, O $\to$ Virtual object
I $\to$ Real image
Hence, option $\left(a\right)$ is the correct answer.