Which is a property of an ideal gas?
a) constant volume of molecules
b) strong intermolecular forces of attraction
c) loss of energy during collisions
d) gain of energy during collisions
e) perfectly elastic collisions

The answer is option E. perfectly elastic collisions.

Let's review each option.

A) constant volume of molecules: No because the volume of the molecules changes with temperature and pressure, as we all know.

B), C) and D) may be analyzed using Kinetic Theory of Gases.

Kinetic Theory of Gases claims that molecules of gases do not interact with each other, this is there are not intermolecular forces of attraction or repulsion. Also Kinetic Theory of Gases claims that collisions in ideal gases are almost perfectly elastic collisions.

Elastic collisions are those where there is no loss (nor gain) of energy during the collision.

So, you see that Kinetic Theory of Gases support option E and rejects options B, C and D.