Speed of Sound in Different Mediums

In which medium does sound travel faster: solid or gas?

Sound travels the fastest in 

The sound of an explosion on the surface of a lake is heard by a boatman $100 \mathrm{m}$ away and a diver $100 \mathrm{m}$ below the point of explosion. Of the two persons mentioned (boatman or diver) who would hear the sound first? And why?

Three persons $A$, $B$ and $C$ made to hear a sound travelling through different mediums as given below:

Who will hear the sound first and why?

In which of the following medium does sound travel faster?

In which of the three media—air, water or iron does sound travel faster at a given temperature?