In which of these materials does sound travel most slowly air, steel, glass, water

Sound travels the slowest through air, and the fastest through steel. This seems counter-intuitive, since sound seems clearer through air than it does through a solid like steel, but there is reasoning behind it. Since steel is a solid, the particles within it are more closely packed than in a liquid like water or the gases in air, in which the particles are farther apart even than the water. Sound waves don't have as much distance to travel between particles in solids as they do in liquids or gases, in which the particles are farther apart. Because of this, the sound waves can travel the quickest through solids. The only reason sound travels more quickly through steel than glass is because steel is a crystalline solid, while glass is an amorphous solid. Without getting into the specifics, the difference between a crystalline and an amorphous solid is that an amorphous solid's particles are farther apart than a crystalline solid's, which is why glass doesn't keep its shape as well as steel does. Because of this, sound travels more quickly through steel.

So, to recap, sound travels through air, steel, glass, and water in the following order, with 1 being the slowest and 4 being the quickest:
1. air
2. water
3. glass
4. steel