Ans it with explanation

The correct answer is option a. We know that when a ray of light enters an optically rarer medium, it goes away from the normal and when it enters an optically denser medium, it goes towards the normal. In the question, as you can see that the ray is going away from the normal on entering medium Y and towards the normal on entering medium X from medium Y. This means that refractive index of medium X is more than the refractive index of medium Y. Now observe that the ray of light, without entering medium Z, suffers total internal reflection in medium Y. But we know that TIR takes place only when ray goes from denser to rarer medium. Therefore the refractive index of medium Y is more than that of medium Z. Hence, option a is correct.