You have discovered a new clear material (magic medium!) You are exploring it's new properties.
The light travels 2.1 x 10^8 m/s. What is the index of refraction for this unknown substance? SHOW YOUR WORK!
The index of refraction (n) is the ratio of the speed of light in a vacuum (c) to the speed of light in the medium (v).
n = c/v
Therefore, n = 2.1 x 10^8 m/s / v
Since the speed of light in the medium is unknown, we cannot calculate the index of refraction.