Answer the following questions related to absolute refractive index and the speed of light:
a. (i) Define absolute refractive index of a medium.
b. (ii) Why is absolute refractive index a pure number without any unit? Give a brief reason.
c. (iii) Describe qualitatively how the speed of light in a medium changes when the absolute refractive index of that medium increases. Support your explanation with one everyday example.