Final answer:
In GMAW, neither oxygen, hydrogen, nor CO₂ should be used for welding. Aluminum is the most suitable option for GMAW.
Step-by-step explanation:
In the given options, neither oxygen, hydrogen, nor CO₂ should ever be used for welding GMAW, not even in trace amounts. GMAW stands for Gas Metal Arc Welding, also known as MIG (Metal Inert Gas) welding. These gases are not suitable for this type of welding as they can cause issues with the weld quality and stability. Instead, gases like argon or a mixture of argon and carbon dioxide are commonly used as shielding gases in GMAW to protect the weld from atmospheric contamination.
Out of the given options, the most appropriate choice for welding GMAW would be D. aluminum. Aluminum can be welded using GMAW, and it requires the use of appropriate filler wire and shielding gas.
Learn more about GMAW welding using suitable gases