Question

light travel fastest through which of the following materials (a) diamond (b) water (c) glass (d) air

Answer 1

light travels fast in AIR medium

it speed in air is 299,792 aprox
hope it is help full

Answer 2

The answer is © glass. As a rule sound travels slowest through gases, faster through liquids, and fastest through solids.

So water and air are not the fastest medium of light to pass fast.  

As it is well known that light travels slow via diamond.

Then the fastest medium out of the four is the glass.

Glass is solid and that is why most compatible for light’s fastest plight.