Answer
Diagram "A" shows the final volume of the balloon for that situation.
Work Step by Step
If we put the balloon in a cold storage, the temperature of the gas will decrease.
According to the Charle's law, the gas volume is directly related to the temperature (at constant pressure). Therefore, if the temperature decreases, the volume of the container will also decrease.
The diagram that represents the decrease on the volume is : "$A$".