Which of the following is not a transverse wave?

$A$ sound wave of frequency $v \text{ Hz}$ initially travels a distance of $1 \text{ km}$ in air. Then,it gets reflected into a water reservoir of depth $600 \text{ m}$. The frequency of the wave at the bottom of the reservoir is $(V_{\text{air}} = 340 \text{ m/s}, V_{\text{water}} = 1484 \text{ m/s})$

Write the equation for the speed of a sound wave in metals.

The temperature at which the speed of sound in air becomes double of its value at $0^oC$ is ...... $K$.

What is the ratio of the velocity of sound in hydrogen $\left(\gamma=\frac{7}{5}\right)$ to that in helium $\left(\gamma=\frac{5}{3}\right)$ at the same temperature? (Molecular weight of hydrogen and helium is $2$ and $4$ respectively)

$A$ source of sound of frequency $600 Hz$ is placed inside water. The speed of sound in water is $1500 m/s$ and in air is $300 m/s.$ The frequency of sound recorded by an observer who is standing in air is .... $Hz$