Everyday science (gases): Identify the gas commonly used to fill party/science balloons. Balloons require a gas that is lighter than air and non-flammable for safety. Choose the correct gas.

Given data

• Balloons need a lift-giving gas that is safe.
• Options include inert and reactive gases.

Concept/Approach
Lift requires a gas less dense than air. Helium is lighter than air and inert (non-flammable), making it the standard choice for balloons. Hydrogen is lighter but flammable—therefore unsafe for general use.

Reasoning
• Air density ≈ 1.225 kg/m³ (at STP); helium ≈ 0.178 kg/m³ → provides buoyancy. • Nitrogen/oxygen/argon are close to or heavier than air; they do not provide useful lift.

Final Answer
Helium