Physics - Geometrical Optics Question with Solution | TestHub

The ray retraces its path when it hits a mirror normally.

Parallel to one mirror, it meets the mirrors at angles $\theta ,2\theta ,3\theta$ in turn.

At the third reflection it must hit normally: $3\theta =90^{\circ }$.

$\theta =30^{\circ }$, so the answer is (B).