in which material medium do light travels with lowest speed
The speed of light varies depending on the medium through which it is traveling. In general, light travels at its fastest speed in a vacuum, which is approximately 299,792 kilometers per second (or about 186,282 miles per second).
However, when light travels through a material medium, such as water, glass, or air, its speed slows down due to the interactions between the light and the atoms or molecules of the medium. This slowing down of light in a medium is referred to as the refractive index of the material.
To answer the question, light travels with the lowest speed in a medium called “Bose-Einstein condensate” (BEC). A Bose-Einstein condensate is a state of matter that occurs at extremely low temperatures when a large number of bosons (particles with integer spin) occupy the same quantum state. In a BEC, the speed of light is significantly reduced compared to its speed in a vacuum or other materials.
It is important to note that Bose-Einstein condensates are a very specialized and controlled medium created in a laboratory setting, and they are not commonly found in nature or everyday materials.