The speed of sound is in the gas is given with this formula:
[tex]v=\sqrt{\frac{\gamma RT}{M}}[/tex]
Where T is the temperature, M is the molar mass of the gas, R is universal gas constant and [tex]\gamma[/tex] is heat capacity ratio.
We can find the speed of the sound in different gasses online ( you could also calculate it using above formula).
[tex]Helium: v_h=1007\frac{m}{s}\\ Air: v_a=343 \frac{m}{s}\\ Carbon Dioxide: v_c=267\frac{m}{s}[/tex]
We know that pitch, wavelength, and speed of the sound are related:
[tex]v=f\lambda[/tex]
Because our wavelentgh is the same the frequency must be different.
[tex]v=f \lambda\\
f=\frac{v}{\lambda}[/tex]
[tex]Helium: f_h=\frac{1007}{2}=503.5Hz\\ Air: f_a=\frac{343}{2}=171.2Hz \\ Carbon Dioxide: f_c=\frac{267}{2}=133.5Hz
[/tex]
