Newton assumed that sound propagation in a gas takes place under which condition?

If $v_m$ is the velocity of sound in moist air and $v_d$ is the velocity of sound in dry air,under identical conditions of pressure and temperature,then:

Two sounding sources send waves at a certain temperature in air of wavelength $50 \ cm$ and $50.5 \ cm$ respectively. The frequency of the sources differs by $6 \ Hz$. The velocity of sound in air at the same temperature is (in $m/s$)

The speed of sound in oxygen $(O_2)$ at a certain temperature is $460 \,ms^{-1}$. The speed of sound in helium $(He)$ at the same temperature will be (assume both gases to be ideal): (in $\,ms^{-1}$)

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

$A$ car is moving with a speed of $72 \,km/h$ towards a hill. The car blows its horn at a distance of $1800 \,m$ from the hill. If the echo is heard after $10 \,s$, the speed of sound (in $m/s$) is: