Which statement correctly describes argon and helium as shielding gases?

• A. They readily react with most metals
• B. They mix easily with oxygen to shield
• C. They will not combine chemically with other materials
• D. They must be cooled to be effective

Answer: (C)

The main idea here is that shielding gases used in GTAW must be chemically inert to protect the weld from the surrounding atmosphere. Argon and helium are both noble gases, so their outer electron shells are full and they don’t readily form chemical compounds with metals or oxides at welding temperatures. This inertness means they simply blanket the weld area, displacing air and preventing oxidation, contamination, or reactions with nitrogen or oxygen.

That’s why the best description is that they will not combine chemically with other materials. It captures the essential reason these gases are chosen for shielding. The other options describe traits that aren’t true—these gases don’t readily react with metals, they don’t shield by chemically mixing with oxygen, and there’s no need to cool them to be effective.