An experiment is designed to test the relationship between the initial height of a basketball before it is dropped to the height of its rebound bounce. the height of the rebound bounce is measured using a scale positioned behind the ball. in the above experiment, which condition would not be controlled?

In general, when designing the experiment, it is desirable to control all thing that can affect the outcome of the experiment. In practice, this is not easily obtainable.
I imagine it would be hard to control the temperature in this experiment. Even though, temperature does affect the ball's bounce. 
Keep in mind that even if you don't control something it still can be measured and then you can use that information to correct your predictions.

You will hear a hissing sound because of the carbon dioxide escaping the can or bottle

Hahahah jsu’s hsjshshsh. shjshshshsh.