Final answer:
The relationship between the radius and volume of a balloon filled with helium can be described as Increases/Increases.
Step-by-step explanation:
The relationship between the radius and the volume of a balloon filled with helium can be described as Increases/Increases. As more helium is added to the balloon, its volume increases proportionally to the increase in radius. This relationship is based on Boyle's law, which states that as the volume of a gas increases, the pressure decreases, allowing the balloon to expand.