____ is relatively easy to ionize and thus is suitable for alternating-current applications and easier starts

• A. Helium
• B. Argon
• C. Nitrogen
• D. Hydrogen

Answer: (B)

Argon is the shielding gas that best supports a stable, easily started arc in GTAW, especially when using alternating current. The arc in TIG welding relies on having a conductive plasma path, and gases that ionize readily help establish and maintain that path as the current polarity reverses in AC. Argon has an ionization energy that allows it to form and sustain the plasma efficiently without the drawbacks of other options. Helium, while it can produce a very hot arc, ionizes less readily and makes starts more challenging; hydrogen and nitrogen are either reactive or not ideal for typical TIG welds and can contaminate the weld or present safety concerns. So argon offers reliable AC performance and easier starts, making it the best choice.