An inflated balloon shrinks when placed in a freezer because the

When an inflated balloon is placed in a freezer, the temperature of the gas inside the balloon decreases. According to the kinetic molecular theory of gases, the average kinetic energy of gas molecules is directly proportional to absolute temperature:

\[\text{Average KE} = \tfrac{3}{2}kT\]

As temperature drops, the gas molecules move more slowly. Slower-moving molecules collide with the walls of the balloon less frequently and with less force, so they exert less pressure on the balloon walls. Since the balloon is flexible, it contracts until the internal and external pressures balance, causing the balloon to shrink.

The other options are incorrect:

• The volume does not increase - it decreases. This option contradicts what is observed.
• The number of gas molecules does not change. The balloon is sealed; no molecules escape or enter.
• Gas molecules never completely stop moving. According to kinetic theory, molecular motion only ceases at absolute zero (0 K), which is not reached in a domestic freezer.

This behaviour illustrates Charles's Law: at constant pressure, the volume of a gas is directly proportional to its absolute temperature (\(V \propto T\)).