Imp Yellow vs Yellow Oxide

How close are they?

ΔE 29.8, loose: different enough that you should pick on purpose. Yellow Oxide is noticeably darker, much more saturated, warmer than Imp Yellow.

Can I use Yellow Oxide instead of Imp Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 30). Yellow Oxide is noticeably darker, much more saturated, warmer than Imp Yellow.

Can I use Imp Yellow instead of Yellow Oxide?

The same difference applies the other way round: Imp Yellow is noticeably lighter, much more muted, cooler.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.