The refractive indices of four substance P, Q, R and S are 1.50, 1.36, 1.77 and 1.31 respectively. The speed of light is the maximum in the substance:
We know that:
Refractive index (n) = Speed of light in air / Speed of light in a medium
According to this formula, speed of light will be maximum in a substance whose refractive index is minimum.
Therefore, speed of light will be maximum in substance S whose refractive index is 1.31.