Hydrogen can be obtained economically as a byproduct in the electrolysis of what?

Hydrogen can be obtained economically as a byproduct in the electrolysis of water. It's mainly obtained in the the manufacture of Chlorine though.

Hydrogen can be obtained economically as a byproduct in the electrolysis of "brine".

A solution of sodium chloride (NaCl)and water (H2O) refers to the brine.The procedure of electrolysis includes utilizing an electric current to achieve a synthetic change and make new chemicals. The electrolysis of brine is a huge scale process used to make chlorine from salt, so  three important chemicals, NaOH, Cl2, H2, can be gotten by electrolyzing brine.