Answer
The amount of buoyant force on an object is the weight of the displaced fluid/air. Their volumes are the same, so the buoyant forces are the same.
The buoyant force is a small fraction of the basketball's weight, so it doesn't lift the basketball off the floor. The same buoyant force acting on the light balloon has a much more noticeable effect.
Work Step by Step
This is discussed on page 271.
