Which is a drawback to the extensive use of solar energy? a. it is nonrenewable and usually unavailable at night. b. it produces toxic pollution. c. it requires equipment and installation that are expensive. d. it is available only at night.

The main drawback to the extensive use of solar energy is

C. It requires equipment and installation that are expensive.

In fact, despite the fact that solar energy is a very clean form of energy (it  does not produce any carbon dioxide or other forms of waste), it is not widely used yet due to the high cost of equipment (e.g. solar panels) and of installation.

the answer is b, have negligible mass

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.