If the speed of light through material Z is

Question

2.5×10^8 m/s, what is this material’s index of
refraction? The speed of light in a vacuum is
3 × 10^8 m/s.

Answer 1

n=c/v

where
n =the index of refraction
c =the speed of light in vacuum
v =the speed of light in a medium

find n

http://physics.info/refraction/

Answer 2

(3x10^8)/x = 2.5 x 10^8

x= 1.2