It 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. Fuel Hydrogen can be used as a fuel. Rockets Since hydrogen is highly flammable, especially when mixed with pure oxygen, it is used as a fuel in rockets. Usually, they combine liquid hydrogen with liquid oxygen to make an explosive mixture. Chemical processes Hydrogen is an essential part of many chemical processes. Acids and bases Hydrogen atoms are in every acid and base. Hydrogen gas is sometimes used directly to create an acid. For example, it is used in the creation of hydrochloric acid: Fertilizer Hydrogen is important in creating ammonia (NH3) for use in making fertilizer. Food and fat Hydrogen gas is used as a hydrogenating agent to for polyunsaturated fats, such as used in margarine. But it is also used in making unhealthy trans-fats that are often used in cookies and other good.