In which medium does sound travel the slowest?

a. salt water

b. fresh water

c. air

d. cast iron

Sound actually travels slower in air. This is because sound is kinetic energy and has to pass from molecule to molecule. In gas the molecules are farther apart taking more time for it to pass, in water the molecules are closer so it takes less time for the sound to get from one molecule to another and with cast iron (since it's very dense) the molecules are very close allowing sound to travel quickly with ease.