Three plane mirrors form an equilateral triangle with each side of...

As we can see, for $\theta = 30 °$, the ray will incident normally and hence will retrace its path, hence the ray will come out for $\theta = 30 °$ and $0 < l < L$.

$⇒ \left(A\right)$ is correct

Considering the symmetry of the situation, we can have:

Thus, for $\theta = 60 °$ and $l = \dfrac{L}{2}$, ray will come out from the setup after two reflections.

$⇒ \left(B\right)$ is correct

Now, when $\theta = 60 °$ and $l = \dfrac{L}{3}$, the ray on entering the setup will suffer five reflections and eventually will come out.

As is clear from the above diagram, ray comes out.

$⇒ \left(C\right)$ is not correct

Also, as is clear from the above diagram, total number of reflections $= 5$.

$⇒ \left(D\right)$ is not correct.