Which of the following waves is used in sonography?

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 $\,ms^{-1}$)

The velocity of sound in air is:

What is the ratio of the speed of sound in nitrogen gas to that in helium gas at the same temperature of $300 \, K$?

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)

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 $m/s$)