The path of a light ray, from air to three different media A, B, and C for a given angle of incidence. The refractive index of B relative to C is

The refractive index of B relative to C is less than 1. 
“Refractive index is the value calculated by the ratio of the speed of the light in a vacuum to that in a second medium of greater density.”
We know that refractive angle and refractive index are inversely proportional to each other. 

As the refractive angle of A> B>C, the refractive indices of$n_a<n_b<n_c$. 

Thus, the ratio of the refractive index of B to the refractive index of C is less than 1.