Answer: When the teacher inflates the balloon with gas at room temperature and then places the balloon into a bucket of ice-water, the volume of the balloon decreases due to the effect of Charles's Law.
Charles's Law states that the volume of a given amount of gas at a constant pressure is directly proportional to its absolute temperature. In other words, as the temperature of the gas decreases, the volume of the gas also decreases, assuming the pressure remains constant.
When the balloon is inflated with gas at room temperature, the gas inside the balloon has a certain volume at that temperature. However, when the balloon is placed in the bucket of ice-water, the temperature of the gas inside the balloon decreases significantly. As a result, the gas molecules in the balloon lose kinetic energy and slow down, causing them to move closer together. This decrease in kinetic energy and the subsequent decrease in molecular motion leads to a reduction in the volume of the gas.
In summary, the volume of the balloon decreases when placed in the bucket of ice-water because the gas inside the balloon cools down, and according to Charles's Law, the volume of the gas is inversely proportional to its absolute temperature at a constant pressure.