Question

The speed of light in substance X is 1.25 × 10⁸ m/s and that in air is 3 × 10⁸ m/s. The refractive index of this substance will be: 

(a) 2.4
(b) 0.4
(c) 4.2
(d) 3.75

Answer 1

2.4 

Refractive index = `"speed of light in air"/"speed of light in the substance"` 

`(3xx10^8  "m/s ")/(1.25xx10^8"m/s")`=2.4