The refractive index of a material is 1.20. if the velocity of light in vaccum is 3 x 10⁸ m/s. the velocity of light in the medium is :
(a) 2.5 x 10⁸ m/s
(b) 2.8 x 10⁸ m/s
(c) 2.4 x 10⁸ m/s
(d) 2.0 x 10⁸ m/s