Why is helium safer to use in a balloon than hydrogen?
Not as flammable but more expensive and less lift-search "Hindenburg"
How to Use valence electron configuration to explain why helium is safer than hydrogen for use in airships?
Contemporary weather balloons are usually filled with helium. Helium is lighter than air, and this allows the balloon to rise as this gas is lighter than air. Hydrogen would also work as it has a low density, like helium. And hydrogen is a bit cheaper than helium because it can be "made" from water. But hydrogen is flammable or even explosive, and it is generally not used for that reason.