Question

what is the most common gas produced by welding electrodes as they burn/melt? oxygen argon carbon dioxide helium

Explanation:

Welding electrodes contain carbon. When they burn/melt, carbon reacts with oxygen (from the air) to form carbon dioxide. Oxygen is a reactant (not a product here), argon and helium are inert gases often used as shielding gases in welding (not produced by electrode burning/melting).

Answer:

carbon dioxide