Which of the following is a common shielding gas used in MIG welding?

Argon is a common shielding gas used in MIG welding primarily because of its inert properties, which make it effective for protecting the weld pool from atmospheric contamination. Inert gases like argon do not react with the molten metal, allowing for a stable arc and reducing the risk of defects in the weld. Additionally, argon provides excellent arc stability and helps produce a smooth, clean weld bead.

In contrast, while oxygen is sometimes used as an additive in certain welding processes to enhance penetration or assist with the welding of specific materials, its presence can lead to oxidation and negatively affect weld quality in MIG welding. Nitrogen is not typically used as a shielding gas in MIG welding due to its potential to form nitrides, which can weaken the weld. Hydrogen, while used in specific applications such as alloy welding, is not generally suitable for MIG welding due to its reactivity, which can lead to embrittlement or defects in the weld. Thus, argon stands out as the preferred shielding gas in MIG welding practices.