Assumptions Of Kinetic Theory

The assumptions underpinning the ideal gas model are laid out explicitly in NCERT Class 11, Chapter 13 (Kinetic Theory). A key postulate is that all collisions, both between molecules and with the container walls, are perfectly elastic, meaning total kinetic energy is conserved and the gas neither gains nor loses energy through collisions. This is essential for the gas to maintain a steady pressure and temperature. The option about strong long-range attractive forces is wrong because the ideal model assumes molecules exert negligible forces except during brief collisions. The option that molecular volume is comparable to container volume is wrong, since the theory assumes molecules are point-like with volume negligible compared to the container. The option that all molecules share one identical speed is wrong because the theory recognises a distribution of speeds described by the Maxwell distribution. A consistency check confirms the choice: elastic collisions preserve kinetic energy so the average molecular energy, and hence temperature, remains constant in an isolated container, which matches the observed stability of an ideal gas in equilibrium.