Four transparent media have refractive indices 1.31, 1.43, 1.33 and 2.40. In which medium does light travel at the greatest speed?

1. Speed in a medium is $v = \dfrac{c}{\mu}$, so $v$ is inversely related to $\mu$. 2. The smallest refractive index gives the largest speed. 3. Among 1.31, 1.43, 1.33 and 2.40, the smallest value is 1.31. 4. So light is fastest in the medium of index 1.31; index 2.40 would give the slowest light. _Source: Samacheer Kalvi (TN SCERT) Class 10 Science, Unit 2 Optics "Refraction of Light", p.24_