Which statement is NOT a postulate of the kinetic molecular theory?

• A. Gases consist of tiny particles.
• B. The volume of the particles is negligible.
• C. The particles attract or repel each other.
• D. The average kinetic energy is proportional to Kelvin temperature.

Answer: (C)

In the kinetic molecular theory, gases are modeled as particles in constant, random motion with no forces acting between them, except during perfectly elastic collisions. This means the particles’ own volume is negligible, collisions conserve kinetic energy, and the average kinetic energy is proportional to the absolute temperature. The statement that particles attract or repel each other goes against this core assumption of no intermolecular forces, so it is not a postulate of the theory. The other points fit the model: tiny particles, negligible particle volume, elastic collisions, and temperature-dependent average kinetic energy. Real gases can show attractions or repulsions under certain conditions, which is why deviations from ideal behavior occur, but those interactions are not part of the idealized postulates.