The exploding hydrogen balloon is a simple chemistry demonstration, yet one that is sure to capture your audience's attention. It's especially useful for illustrating the difference between hydrogen and helium. Both gases are lighter than air and produce a floating balloon, yet if you touch a match to the helium balloon, all that happens is that the balloon pops. Helium is a noble gas and non-reactive. As you can see, the effect is a tiny bit more dramatic when the balloon contains hydrogen gas. All you need is a balloon and some hydrogen... Here's what you do.
Don't want to try it yourself? You can catch this demonstration live at many museums, such as Chicago's Museum of Science and Industry, which is where I took this photo.