The Kinetic theory can NOT be used to explain

1. Analyze the question We are asked which phenomenon the kinetic theory of matter cannot explain.

2. The concept The kinetic theory says matter is made of tiny particles that are in constant random motion. The particles have kinetic energy that increases with temperature, and there are attractive forces between them that differ across solids, liquids and gases.

3. Check each option

• A. Allotropy: This is the existence of an element in different structural forms in the same physical state, e.g. diamond and graphite (carbon), or rhombic and monoclinic sulphur. It depends on how atoms are bonded and arranged in the structure, not on particle motion. The kinetic theory does not explain it.
• B. Brownian movement: This is the random zigzag motion of colloidal or pollen particles. It is caused by collisions with fast-moving molecules of the medium, which is direct evidence for the kinetic theory.
• C. Diffusion: Particles move randomly from regions of high concentration to low concentration. The kinetic theory explains this.
• D. Tyndall effect: This is the scattering of light by colloidal particles. Strictly, it is an optical phenomenon explained by light scattering. In many textbook treatments, though, it is linked to colloids and Brownian motion, and it is a less direct case than allotropy.
• E. Vaporization: Molecules at the liquid surface gain enough kinetic energy to overcome intermolecular attractions and escape. The kinetic theory explains this.

4. Working out the answer The Tyndall effect is a light-scattering phenomenon, so it could also be argued as "not explained" by the kinetic theory. However, allotropy is the clearest case: it is about differing atomic arrangements and bonding in the solid, which has nothing to do with the motion of particles.

Answer: A. allotropy

5. Exam tip Kinetic theory is about particle motion and energy: diffusion, Brownian motion, vaporization, gas pressure. If a phenomenon is about structure or arrangement of atoms (allotropy, isomerism), the kinetic theory is not the explanation.