This is the speed of light in vacuum divided by the speed of light in the medium. this determines the amount of bending of a light wave

Refractive index.

Explanation:

Refractive index or the index of refraction may be defined as the quantity that measures how fast the light travels in different media. Different materials have different refractive index.

Refractive index can be calculated by the formula by dividing the speed of light in vacuum with the speed of light in different media. The amount of refraction and the bending of light as light enters from one media to another is shown by the refractive index.

Thus, the answer is refractive index.

c. earths continental crust is thicker than its lithosphere.

because, the lithosphere is the outermost layer of the earth/ 100 km thick and is defined by its machanical properties.the lithosphere contains oceanic and continental crust that varies in age and thickness across locations and geologic time. the lithosphere is the coolest layer of the earth in terms of temperature. the term lithosphere should not be confused with the use of "geosphere" which is used to indicate all of earth systems, including the atmosphere, hydrosphere   and biosphere. the surface of the earth can be divided into the continental crust and the oceanic crust.   the continental crust is made mostly of granite while the oceanic crust is made of basalt. the average thickness of the continental crust is 25 miles and the average thickness of the oceanic crust is 5 miles.   three types of rock, igneous, sedimentary, and metamorphic, make up the surface of the earth. that's why 3 option is preferable.