List three important uses of hydrogen.

Three important uses of hydrogen are:
i. Hydrogen is mainly used in the manufacture of ammonia, which is further used to prepare fertilisers like urea, ammonium sulphate etc.
ii. It is used in the extraction of metals such as copper, lead, tungsten, tin; for example, hydrogen is used as a reducing agent in the reduction of tungsten oxide to purify tungsten during extraction.
iii. It is used in cutting and welding of metals in industries. When hydrogen is burnt in oxygen, an oxy-hydrogen flame is obtained by which cutting and welding of metal is performed.