✔ 最佳答案
Both CO2 and air are gases. In a gas, sound wave travels faster in the one that has a lower density.
Sound waves travel through a medium by the transmissionof vibrations. Thus, media that are more stiff transmit sound wave faster than those less stiff ones. The degree of stiffness is measured by a term called "Modulus of Elasticity".
Solid has a "Modulus of Elasticity" much much higher than that of gases. This is why sound wave travels faster in solids than in gases.
However, the "Modulus of Elasticity" for gases are about the same at the same temperature and temperature. In that case, the speed of sound is higher in low density gases because their molecules vibrate faster than high density gas molecules.