As the temperature of the gas in a balloon decreases which occurs after

The Ballon will shrink.

Explanation:

Temperature is the measure of the average kinetic energy of the air molecules within the Ballon. As the temperature is gradually reduced, the molecules lose kinetic energy and their movement around the Ballon reduces which reduces the rate at which they collide with the Ballon walls. As the temperature drops further, the molecules comes even more closer since they can't move around any further causing the Ballon to shrink.