1. Yes – sound can travel through a
balloon filled with hydrogen. However you will notice two differences between this
case and when sound waves travel through air. First the speed of sound in hydrogen
is greater than that in air at the same pressure because the molecules of hydrogen
are lighter than those of air. Secondly the balloon will act like a lens and change the
direction of the sound. Because of the greater speed of sound in hydrogen the lens
effect will be similar to a concave lens in light.
2. No - sound cannot pass
directly between twp space shops because sound requires a material (gases, liquids
or solids) to travel through and there will be no material between these two
spaceships out in space. (Strictly there may be some matter but the density will be so
incredibly low that we can ignore it for all practical situations).