1) As it is highly inflammable,Hydrogen can be used in rockets as fuel,usually they combine pure liquid hydrogen with liquid oxygen to form an explosive mixture

2)But also,hydrogen is one of the cleanest fuels because when it burns, the result is simple water. That is why there are efforts to create engines that can power automobiles on hydrogen.
Hydrogen is the lightest element and can be used as a lifting agent in balloons. Since Hydrogen gas is highly flammable, it can be dangerous to use. But this property and others make Hydrogen suitable for use as a fuel. The most common use of Hydrogen is in chemical processes and reactions.