Answer:1.68.
Step-by-step explanation:The index of refraction of a substance can be calculated using the formula:
index of refraction = speed of light in vacuum / speed of light in the substance
The speed of light in vacuum is 3.00 x 10^8 m/s, and the speed of light in the unknown medium is 1.79 x 10^8 m/s.
index of refraction = 3.00 x 10^8 m/s / 1.79 x 10^8 m/s = 1.68
Therefore, the index of refraction for the unknown substance is 1.68.