What is a longitudinal wave?

If the frequency of a tuning fork is $400 \, Hz$ and the speed of sound in air is $340 \, m s^{-1}$,find how far sound travels when the tuning fork makes $16$ vibrations. (in $, m$)

If the density of a medium through which sound is propagating is minimum,then this point is called:

$(a)$ The sound of an explosion on the surface of a lake is heard by a boatman $100 \ m$ away and a diver $100 \ m$ below the point of explosion. Of the two persons mentioned (boatman or diver),who would hear the sound first and why?
$(b)$ Calculate the wavelength of a sound wave whose frequency is $220 \ Hz$ and speed is $440 \ m \ s^{-1}$ in a given medium.

$(a)$ $A$ particular transmitter of Aakashvani broadcasts at $420.5\, m$ wavelength. Given the speed of radio waves $3 \times 10^{8}\, m s^{-1}$. Calculate the frequency at which the radio station broadcasts its programme.
$(b)$ What is the direction of oscillations of the medium particles through which a
$(i)$ transverse wave is propagating?
$(ii)$ longitudinal wave is propagating?

$(i)$ Even if a loud explosion were to take place at any place on the moon,it would not be heard at a nearby point. Give reason.
$(ii)$ Explain in brief the dependence of speed of sound on the nature of the material medium and temperature.
$(iii)$ Identify the two factors on which the loudness of sound depends.