Correct Answer:
C. Acetylene
The question asks about the gas commonly used in welding. Acetylene (C2H2) is the correct answer because it is a highly combustible hydrocarbon gas that, when combined with oxygen in an oxy-fuel torch, produces an extremely hot flame (up to 3,500 °C or 6,330 °F). This intense heat is ideal for melting and joining metals, making it a primary fuel gas for various welding and cutting applications.
- Hydrogen can be used in some specialized welding processes, but it does not achieve the same high temperatures as oxy-acetylene and is not as universally applied for general welding.
- Nitrogen is an inert gas primarily used as a shielding gas in certain welding techniques to prevent atmospheric contamination, not as a fuel gas to generate heat.
- Therefore, 'all' is incorrect as hydrogen and nitrogen do not serve the same primary fuel purpose as acetylene in common welding practices.