Final answer:
Electrolysis is the process of decomposing substances using a direct electric current. When hydrogen and air are mixed and ignited, it produces a pale blue flame.
Step-by-step explanation:
The process in which substances such as hydrochloric acid are decomposed by a direct electric current is called electrolysis. In this process, an electric current is passed through an electrolyte, such as hydrochloric acid, causing the constituent ions to move towards the electrodes. At the cathode, hydrogen ions gain electrons to form hydrogen gas.
When a burning splint is applied to a mixture of hydrogen and air in a test tube, the hydrogen gas combusts vigorously in the presence of oxygen from the air. This reaction produces water vapor and releases a significant amount of heat. The resulting flame is pale blue and almost invisible.
Learn more about Electrolysis and combustion