ideal gas vs real gas

The statement is correct for ideal gas, but the answer "......molecules lose KE during collisions, producing sounds" is surely not correct.

If what was given by the answer is right, then we would expect there is sound emitted from a balloon (which is filled with air, hydrogen or helium), as collisions between molecules in real gases are not perfectly elastic. This is clearly not the case in real life.

Another point is that sound is in fact an orderly vibration of gas molecules. Collisions between molecules in a gas are random. How come this would result in an orderly vibration of the molecules to produce sound.

In a real gas, molecular collisions lead to an exchange between the translational kinetic energy of molecules and their internal degrees of freedom (which is just the rotational or vibrational energy of molecules). Hence, translational kinetic energy may not be conserved and the collision is inelastic.

You could refer to the following web-page (read the 3rd para.):

http://en.wikipedia.org/wiki/Inelastic_collision