Hydrogen is used in oxy-hydrogen flames for melting metals because it

Hydrogen is used in oxy-hydrogen flames for melting metals because it evolves a lot of heat when burnt. When hydrogen gas is burned in the presence of oxygen, it undergoes a highly exothermic reaction to form water vapor. The heat released during this reaction is intense and can be used to melt metals, such as gold, silver, and copper. This process is known as oxy-hydrogen welding, and it is commonly used in jewelry making, metal sculpture, and other metalworking applications. While hydrogen can be explosive when mixed with air or oxygen in certain conditions, oxy-hydrogen welding relies on the controlled burning of hydrogen in the presence of oxygen to generate heat for melting metals. Hydrogen is also a very light gas, but this property is not relevant to its use in oxy-hydrogen flames for melting metals. Additionally, while hydrogen can be used as a rocket fuel, this is not related to its use in oxy-hydrogen welding.