Which of the following statements is wrong?

An underwater sonar source operating at a frequency of $60 \, kHz$ directs its beam towards the surface. If the velocity of sound in air is $330 \, m/s$,the wavelength and frequency of waves in air are:

$A$ $SONAR$ (sound navigation and ranging) uses ultrasonic waves to detect and locate objects under water. In a submarine equipped with a $SONAR$,the time delay between generation of a probe wave and the reception of its echo after reflection from an enemy submarine is found to be $77.0\; s$. What is the distance of the enemy submarine (in $; km$)? (Speed of sound in water $= 1450\; m/s$)

What is called compression or condensation? Which type of changes in density and pressure take place in it?

$A$ string is stretched so that its length is increased by $\frac{1}{\eta }$ of its original length. The ratio of the fundamental frequency of transverse vibration to that of the fundamental frequency of longitudinal vibration will be

$A$ plane sound wave passes from medium $1$ into medium $2$. The speed of sound in medium $1$ is $200 \, m/s$ and in medium $2$ is $100 \, m/s$. The ratio of the amplitude of the transmitted wave to that of the incident wave is: