The law of conservation of energy is a statement that : energy must be conserved and you are breaking a law if you waste energy.
the total amount of energy is constant for a closed system.
the supply of energy is limited so we must conserve.
energy can be used faster than it is created.
energy cannot be used faster than it is created.

option  B

Explanation:

The correct answer is option  B

From the option given option B describes law of conservation of energy which is total amount of energy is constant for closed system.

law of conservation of energy stated that energy cannot be created nor be destroyed but it can transformed from one form to another.

rest options are not correct as they does not follow the statement of the energy conservation.

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.