What is the index of refraction?

a. the ratio of the speed of light in a vacuum to the speed of light in the material it is passing though

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 ray enters the new medium and the angle at which it is reflected

d. the percentage that the light ray bent when it entered the new medium

a. the ratio of the speed of light in a vacuum to the speed of light in the material it is passing though    

Explanation:

When a light ray enters from one medium to another, it bends. This is because the speed of light decreases as it enters a medium having more optical density. The speed of light is maximum in vacuum.

The refractive index determines the optical density of a medium. It is the ratio of the speed of light in the vacuum (c) to the speed of light in the material it is passing through (v).

answer: 802.3 kilo joules of energy represents 191.75 kilo calorie of energy.

explanation:

energy released during combustion of one mole methane = 802.3 kilo joules

if 1 kilo joule = 0.239006   kilo calorie

then ,802.3 kilo joule will be = 802.30.239006 kilo calorie

802.3 kilo joule = 191.75 kilo calorie

hence, the energy in kilo calorie is 191.75 kilo calorie.