Which gas is produced during electrolysis of brine, that burns with a pop sound?

During the electrolysis of brine (a concentrated solution of NaCl), hydrogen gas (H2) is produced as a byproduct. Hydrogen burns with a distinctive pop sound when ignited. This process also produces chlorine gas (Cl2) and sodium hydroxide (NaOH). In the chlor-alkali industry, hydrogen is often combined with chlorine to produce hydrochloric acid (HCl).