The speed of light is minimum while passing through a medium such as glass, water, or any other material other than a vacuum.

In a vacuum, the speed of light is considered to be its maximum value, which is approximately 299,792 kilometers per second (or about 186,282 miles per second). Light travels at this maximum speed in a vacuum because there are no particles or atoms to interact with and slow it down.

When light passes through a medium such as glass, water, or air, it interacts with the atoms or molecules of that medium, which causes it to slow down. This slowing down of light is due to the absorption and re-emission of photons by the atoms or molecules of the medium.

Among the options provided:

- Glass: Light slows down when passing through glass. The refractive index of glass is higher than that of air, which causes the speed of light to decrease as it enters and passes through the glass.

- Vacuum: In a vacuum, there is no medium to interact with, so the speed of light is at its maximum value.

- Water: Light also slows down when passing through water. The refractive index of water is higher than that of air, causing a decrease in the speed of light as it enters and travels through the water.

- Air: Light also slows down when passing through air, although the difference in speed compared to a vacuum is relatively small. The refractive index of air is slightly higher than that of a vacuum, resulting in a slightly slower speed of light.

In summary, the speed of light is minimum while passing through a medium such as glass, water, or any other material other than a vacuum.