Nitrogen
Helium
Oxygen
Argon
Answer is Wrong!
Answer is Right!
The correct answer is B. Helium.
Helium is a gas that is lighter than air. This means that it will float up in the air. Balloons are filled with helium so that they will float.
Nitrogen is a gas that is heavier than air. This means that it will sink in the air. Balloons are not filled with nitrogen because they would not float.
Oxygen is a gas that is essential for life. It is not used to fill balloons because it is not lighter than air.
Argon is a gas that is heavier than air. It is not used to fill balloons because it is not lighter than air.