air:
@Felthry Ooooh we're torn between 2 and 4 but probably 4.
@Felthry voted 20% oxygen etc after thinking about it a bit, because dive mixtures like trigas and heliox are breathable but I definitely wouldn't call them air.
but if I was on a spaceship filled with some earthlike gas mix, I'd say "yeah the cabin has air in it".
@Felthry I could see myself reasonably calling some very non-terran atmosphere of another planet "air", but it'd be pretty contextual.
@Felthry but ultimately if someone said "air" when casually referring to any of the options, I wouldn't be mad at it.
@Felthry (btw divers on heliox is great because these are professionals doing something exceedingly dangerous with squeaky voices the entire time)
@Felthry (oh I misstated earlier, the gas mix I was thinking of is called "trimix", not "trigas".)
air: