Question

Which of the assumptions of the kinetic-molecular theory best explains the observation that a balloon collapses when exposed to liquid nitrogen (which is much colder than a cold winter day)?

• A. Gas molecules move at random with no attractive forces between them.
• B. The velocity of gas molecules is proportional to their kelvin temperature.
• C. The amount of space occupied by a gas is much greater than the space occupied by the actual gas molecules.
• D. Collisions with the walls of the container or with other molecules are elastic.

Answer 1

The correct option is B

The velocity of gas molecules is proportional to their kelvin temperature.

All the options belong to the postulates of Kinetic theory of gases.
Kinetic Energy $\propto$ Temperature

As cold nitrogen comes in contact with the balloon surface, assuming the balloon is intact, it collapses. Due to heat transfer, nitrogen takes away the heat from the gas molecules inside the balloon. As temperature decreases, KE decreases.

This also reduces the velocity with which gas particles move. Thus the pressure exerted by the gas from the inside decreases. So, balloon collapses.