When an inflated balloon is placed in a freezer, the temperature of the gas inside decreases. According to the kinetic molecular theory and Charles's Law:

Gas molecules lose kinetic energy and move more slowly. This reduced motion results in less frequent and less forceful collisions with the inner walls of the balloon. The overall effect is a decrease in the internal pressure of the gas. Since the external atmospheric pressure remains constant, the balloon is compressed and shrinks in volume until the internal and external pressures equalize, resulting in a smaller balloon.