Question

The value for the index of refraction for any material must be

Answer 1

Larger than one.

In fact, the index of refraction of a medium is the ratio between the speed of light in vacuum (c) and the speed of light in that medium (v):

`n= (c)/(v)`
But the maximum speed the light can travel at is exactly c, the speed of light in vacuum: so v is always less (or equal, in case of vacuum) than c, and so n is always greater than 1.