Here's why:

* The speed of light is fastest in a vacuum. This is considered the theoretical maximum speed of light.

* Light slows down when it travels through matter. This is because light interacts with the atoms and molecules in the material.

* The denser the material, the slower the light travels.

Therefore, the materials listed in order of increasing speed of light would be:

1. Fused quartz (highest density)

2. Crown glass

3. Water

4. Air (lowest density, closest to a vacuum)