Noble gases are inert due to how they have a fulloutershell.
Helium can be used in party balloons and airships because it is less dense than air and therefore floats. Because it is inert, it is non-flammable so it isnt dangerous.
Argon, Krypton and Xenon can be used in filament lamps. The metal filament can become hot enough to burn out, so these inertgases stops this.
Argon can be used during welding to keep air away because it is denser. The metal does not oxidise, due to its shieldingeffect.
