- Helium is less dense than air
- A balloon is a kind of container
- A balloon is filled with helium gas
- Hence, a balloon filled with helium is an example of a container contains a substance less dense than air

- A balloon filled with helium is an example of a container contains a substance less dense than air
- If a container contains a substance with less density than air then that container may move upward
- Hence, the balloon filled with helium may move upward if released

Therefore, the balloon filled with helium may move upward if released
Question: A balloon filled with helium gas is set free and starts to move upward. Which of the following best explains why the helium balloon moves upward?
Context: - Helium is less dense than air 
- If a container contains a substance with less density than air then that container may move upward 
- A balloon is a kind of container 
- A balloon is filled with helium gas