The index of refraction of a material is the ratio between the speed of light in vacuum, c, and the speed of light in that material, v:
[tex]n= \frac{c}{v} [/tex]
where the speed of light in vacuum is [tex]c=3 \cdot 10^8 m/s[/tex]. The speed of light in benzene is [tex]v=2.00 \cdot 10^8 m/s[/tex], so we can use the previous relationship to find the refractive index of benzene:
[tex]n= \frac{3 \cdot 10^8 m/s}{2.00 \cdot 10^8 m/s}=1.5 [/tex]
