Solution:

According to the kinetic theory of gases:

- (A) Collisions are always elastic: Gas molecule collisions do not lose kinetic energy, so they are elastic.
- (B) There is no force of attraction among the molecules: Assumption of ideal gases is no intermolecular forces.
- (C) Only a small number of molecules have very high velocity: Most molecules have moderate speeds; only a few have very high speeds.
- (D) Between collisions, the molecules move in straight lines with constant velocities: Molecules move with constant speed in straight lines until they collide.

All options are correct as per the assumptions of kinetic theory.