What property of hydrogen is shown in the result

Question

Invert an empty testube over a testube of hydrogen gas and hold them mouth to mouth for several seconds. Prepare 2 burning splinter and thrust at the same time to each tube.

Answer 1

The top one will "pop" and the bottom one will do nothing. The Hydrogen in the lower tube has moved to the top tube. This demonstrates that Hydrogen at the same temperature and pressure is less dense than air.