(N/A) The largest single use of $Dihydrogen$ is in the synthesis of ammonia,which is used in the manufacture of nitric acid and nitrogenous fertilizers.
$Dihydrogen$ is used in the manufacture of vanaspati fat by the hydrogenation of polyunsaturated vegetable oils like soyabean,cotton seeds,etc.
It is used in the manufacture of bulk organic chemicals,particularly methanol:
$CO_{(g)} + 2H_{2(g)} \xrightarrow{\text{cobalt catalyst}} CH_3OH_{(l)}$
It is widely used for the manufacture of metal hydrides and for the preparation of hydrogen chloride,a highly useful chemical. In metallurgical processes,it is used to reduce heavy metal oxides to metals.
$Dihydrogen$ is used in fuel cells for generating electrical energy. It has many advantages over conventional fossil fuels and electric power,as it does not produce pollution and releases greater energy per unit mass of fuel compared to gasoline.
Atomic hydrogen and oxy-hydrogen torches are used for cutting and welding. Atomic hydrogen atoms (produced by dissociation of $Dihydrogen$ using an electric arc) are allowed to recombine on the surface to be welded,generating temperatures up to $4000 \ K$.