Yes. When you burn hydrogen the product is water. If you pass an electric current through that water you can split it back into hydrogen and oxygen.
All stars 'burn' hydrogen
helium does not burn, hydrogen will burn in air
Hydrogen gas is highly flammable; you can make it burn with the slightest spark.
No hydrogen will not burn in the absence of air unless another oxidizer is present.
You don't. Sea water is the combustion byproduct of hydrogen. That is, water is water you get when you burn hydrogen.
Water.
yes
Burn hydrogen
Hydrogen burn in air releasing a typical sound.
burn it?
yes
All main sequence stars fuse hydrogen.