Correct option is C
In arc welding, shielding gases are used to protect the weld area from atmospheric gases like oxygen, nitrogen, and water vapor, which can cause weld defects such as porosity and oxidation. Common shielding gases include inert gases like argon and helium, as well as carbon dioxide, which is often used in metal inert gas (MIG) welding. Carbon monoxide, however, is not used as a shielding gas because it is toxic and does not provide the necessary protection against atmospheric contamination in the welding process.
