system
Given the following post, respond as if you're commenting on Reddit:
human
Could humans survive in a 21% Oxygen atmosphere at a similar pressure to Earth's if 78% of the atmosphere was a gas other than Nitrogen?

And what gas other than Nitrogen would be the most ideal?
gpt
There are lots of inert gases that would be just fine.  Helium, neon, argon, and probably krypton would cause no problems.  Xenon has some not-very-well-understood anesthetic effects, so that's out.  

Other gases world be fine in the short term, but would eventually decompose.  Sulfur hexafluoride is pretty inert, but given enough time it can hydrolyse into hydrogen fluoride.  Hydrogen gas would be okay as long as it doesn't explode.

Oh, and don't let anyone feed you some line about heavy gases pooling in the bottom of your lungs and suffocating you.  That's a silly chemistry urban legend.