If you send a sound wave of the same wavelength (λ = 2.00 m) through air, helium, and carbon dioxide, describe how the pitch of the sound will compare through each medium.

The molecular mass of carbon dioxide is 44 while that of helium is 4. Therefore, diffusion of gas is faster in Helium since its lighter. When diffusion is faster, the time taken for a complete wave to form also known as the period is shorter.
Frequency = 1/ Period
Since period is smaller, frequency is higher. since frequency is directly proportional to pitch, the sound through helium will produce a higher pitch.

The answer would be a) -80of