Which gas is described as relatively easy to ionize and suitable for AC starts?

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

Answer: (B)

Argon is described this way because it ionizes readily enough to form the conductive plasma arc needed for TIG welding, and it does so in a way that supports starting and sustaining the arc on alternating current. When starting an AC TIG arc, the shielding gas must become ionized to carry the current between electrode and workpiece without introducing contamination. Argon provides a stable, responsive arc and effective shielding, making AC starts more reliable. Helium, while usable, requires higher starting voltage and is more expensive and hotter, which can complicate starts. Nitrogen isn’t used as a shielding gas in GTAW due to reactivity and weld contamination concerns, and hydrogen can cause porosity or embrittlement and is generally avoided as a primary shielding gas. So, argon best fits the description of being relatively easy to ionize and suitable for AC starts.