500
The Hindenburg was a zeppelin (blimp) that was designed to transport passengers much like an airplane. However, upon landing, it caught fire and exploded. The Hindenburg used hydrogen gas (H2). Explain in thorough detail WHY this was a poor idea AND what other (safer) element could have been used for the same purposes.
The hydrogen atoms readily combined with other elements by donating an electron, and therefore caused a large fire (as the chemical reaction released energy). Helium would have been a safer alternative, as it is a noble gas (not likely to bond with other elements), and is still lighter than air.