Which gas is not used as a welding agent?

• A. Acetylene
• B. Natural gas
• C. Carbon dioxide
• D. Hydrogen

Answer: (C)

Carbon dioxide is primarily used as a shielding gas in welding processes, rather than as a fuel or welding agent. It is often used in Gas Metal Arc Welding (GMAW) and Flux-Cored Arc Welding (FCAW) to protect the molten weld pool from atmospheric contamination.

In contrast, acetylene is widely recognized as a fuel gas in oxyacetylene welding, where it combines with oxygen to create a high-temperature flame suitable for melting metals. Natural gas also serves as a fuel gas in welding applications, particularly in some oxy-fuel welding setups. Hydrogen, while less common, can be used in specialized welding processes, including some types of fusion welding, where its high flame temperature is beneficial.

Thus, the primary distinction lies in the application of carbon dioxide as a shielding gas rather than a welding agent in the same way that acetylene, natural gas, or hydrogen are used as fuel gases in the welding process.