If a mineral causes light to slow down by 20 then a The wave

If a mineral causes light to slow down by 20% then a. The wavelenth must decrease by 20%
b. The wavelenth must increase by 20%
c. The frequency must decrease by 20%
d. The frequency must increase by 20%
e. The amplitude must increase by 40%

Solution

a. The wavelenght must decrease by 20%.