Question

Light is transmitted the fastest through ______________? Water Air Cheese Vacuum (outerspace)

Answer 1

vacuum.
The speed of light in a vacuum is the universal constant c, which is
2.998 * 10^8 meters/second.

Now, in any medium (e.g. air, water, or glass, etc.), light will travel
slower than this. This is because light is essentially an electromagnetic
wave, and the transmission of this wave depends on the electrical
characteristics and density of the medium it is passing through.
for more reading http://www.madsci.org/posts/archives/1997-12/878700157.Ph.r.html

Answer 2

Ask these questions in Physics, not Social Sciences. This is for law, communications, psychology, sociology, and the like.