What is the phase difference between the displacement wave and the pressure wave in a sound wave?

$A$ man standing on a cliff claps his hands and hears the echo after $1 \, s$. If the sound is reflected from another mountain and the velocity of sound in air is $340 \, m/s$,then the distance between the man and the reflection point is ..... $m$.

The Earth has a radius of $6400 \ km$. The inner core of $1000 \ km$ radius is solid. Outside it,there is a region from $1000 \ km$ to a radius of $3500 \ km$ which is in a molten state. Then again from $3500 \ km$ to $6400 \ km$,the Earth is solid. Only longitudinal $(P)$ waves can travel inside a liquid. Assume that the $P$ wave has a speed of $8 \ kms^{-1}$ in solid parts and of $5 \ kms^{-1}$ in liquid parts of the Earth. An earthquake occurs at some place close to the surface of the Earth. Calculate the time after which it will be recorded in a seismometer at a diametrically opposite point on the Earth if the wave travels along the diameter.

The ratio of densities of nitrogen and oxygen is $14:16$. The temperature at which the speed of sound in nitrogen will be the same as that in oxygen at $55^oC$ is ..... $^oC$.

Sound velocity is maximum in

If at the same temperature and pressure,the densities of two diatomic gases are respectively $d_1$ and $d_2$,then the ratio of the velocities of sound in these gases will be