Ultrasonic waves are those waves

What is the velocity of a wave in a monoatomic gas having a pressure of $1 \, kPa$ and a density of $2.6 \, kg/m^3$?

The ratio of the speed of sound in helium gas to that in nitrogen gas at the same temperature is $\left(\gamma_{He}=\frac{5}{3}, \gamma_{N_2}=\frac{7}{5}, M_{He}=4, M_{N_2}=28\right)$

Match the following:

Column-$I$	Column-$II$
$(a)$ Transverse wave through a steel rod	$(i)$ $\sqrt{B + \frac{4}{3} \frac{\eta}{\rho}}$
$(b)$ Longitudinal waves in earth's crust	$(ii)$ $\sqrt{\frac{\eta}{\rho}}$
$(c)$ Longitudinal waves through a steel rod	$(iii)$ $\sqrt{\frac{2 \pi T}{g \lambda}}$
$(d)$ Ripples	$(iv)$ $\sqrt{\frac{Y}{\rho}}$

$A$ firecracker exploding on the surface of a lake is heard as two sounds a time interval $t$ apart by a man on a boat close to the water surface. Sound travels with a speed $u$ in water and a speed $v$ in air. The distance from the exploding firecracker to the boat is

$A$ man stands in front of a hillock and fires a gun. He hears an echo after $1.5\, s$. The distance of the hillock from the man is ...... $m$ (velocity of sound in air is $330\, m/s$).