Respuesta :
EM waves travel fastest through gas, since the particles are more spread out, and least, since the particles are packed together. Liquids would be average speed. I would say choice A, since B is a liquid, C is a vacuum (no matter), and D is a solid.
Light travel fastest in outer space, therefore the correct answer is option C.
We know that in outer space there is complete vacuum which means there is nothing to obstruct the path of light waves. Where as in swimming pool there is water that obstruct the light waves, in room there are air particle which obstruct the light waves, and in railroad track there is steel molecules which obstruct the path of light waves.
Therefore light waves travel faster in outer medium.