Hydrogen is obtained when an acid reacts with metals. For example, when zinc reacts with hydrochloric acid zinc chloride and hydrogen gas are produced. In industries hydrogen gas is obtained from hydrocarbons. When water reacts with CH3 (methane), hydrogen gas is released with the formation of Carbon mono oxide. When a voltage is applied to water, hydrogen gas is produced at the cathode. This process is known as electrolysis of water. Moreover, hydrogen gas is produced as a byproduct of many chemical reactions.