what is the index of refraction?
(a) the percentage that the light ray bent when it entered the new medium
(b) the amount the light ray has bent toward the normal line when entering a new medium
(c) the difference between the angle at which the light enters the new medium and at the angle and which it is reflected
(d) the ratio of the speed of light in a vacuum to the speed of light in the material it is passing though

The correct answer is ''the ratio of the speed of light in a vacuum to the speed of light in the material it is passing though".

Explanation:

Refractive index is defined as the ratio of the velocity of light travelling in a vacuum to the velocity of light  travelling in a particular medium.

It is dimensionless quantity. It describes how the fast light travels through the material. It measures the bending of a light when it passes from one medium to another.

The expression for the refractive index is as follows:

Here, c is the velocity of the light in vacuum, v is the velocity of light in medium and R.I is the refractive index.

Therefore, the correct option is (d).

a gas, having a molecular weight of 13 kg/kmol and a kinematic viscosity of 0.25 cm2/s, flows through a pipe 0.25 m internal diameter and 5 km long at the rate of 0.4 m3/s and is delivered at atmospheric pressure.