If you decrease the volume of gas in a balloon from 10 liters to 5 liters, the number of collisions of the gas molecules with the balloon walls increases. This is due to Boyle's Law, which shows an inverse relationship between volume and pressure at constant temperature, leading to higher pressure.
When you have a 10 liter sample of gas in a balloon and you apply pressure to decrease the volume to 5 liters, while keeping the temperature constant, the number of collisions between the gas molecules and the walls of the balloon will increase. This is a direct consequence of Boyle's Law, which states that the pressure and volume of a gas have an inverse relationship at a constant temperature. As the volume decreases, the molecules have less space to move around and therefore collide with the walls more frequently, increasing the pressure. This is commonly observed in a gas compression situation where reducing the volume without changing the temperature will result in a higher pressure inside the balloon.