Acetylene is the only fuel gas suitable for gas welding because of its favourable flame characteristics of both high temperature and high propagation rates. Other fuel gases, such as propane, propylene or natural gas, produce insufficient heat input for welding but are used for cutting, torch brazing and soldering.

The correct answer is Oxygen and acetylene. Gases used in welding are Oxygen and acetylene. Oxy-acetylene welding is a very common welding process. In oxy-acetylene welding, the flame produced by the combination of the gases melts the metal faces of the workpieces to be joined, causing them to flow together.

Gases produced from welding and cutting processes include: carbon dioxide from the decomposition of fluxes. carbon monoxide from the breakdown of carbon dioxide shielding gas in arc welding. ozone from the interaction of electric arc with atmospheric oxygen.