Argon

Argon is a colorless, odorless noble gas that rarely reacts with other elements. It makes up about 0.93% of dry air, making it the third most abundant gas there after nitrogen and oxygen. Industry obtains argon by cooling air until it becomes liquid, then separating its components by their different boiling points. Argon's full outer electron shell explains its low reactivity, which is useful when other materials need protection. In welding, a stream of argon shields hot metal from reactions with the surrounding air. Argon also fills the spaces between panes in some energy-efficient windows, helping to slow heat loss because it conducts heat poorly.