Shielded Metal Arc welding uses __________ to protect the weld area from contaminants.

Shielded Metal Arc Welding (SMAW), commonly known as stick welding, uses flux to protect the weld area from contaminants. The flux is a material that melts during the welding process and forms a protective layer over the molten weld pool. This layer helps to shield the weld from atmospheric elements like oxygen and nitrogen that could contaminate the weld and weaken its integrity. Additionally, the flux also contributes to the weld's stability and can help to stabilize the arc during the welding process.

The other substances listed, such as oxygen gas, argon, and carbon dioxide, are not used in the same manner to protect the weld area in SMAW. Oxygen, for instance, can lead to oxidation of the weld, causing weaknesses. Argon is typically used in gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) as a shielding gas but is not relevant in SMAW, which primarily relies on the protective nature of flux. Carbon dioxide can be used as a shielding gas in certain welding processes but does not apply to SMAW either. Therefore, the use of flux in shielded metal arc welding is essential for maintaining the quality of the weld by protecting it from environmental contaminants.