What polyatomic ion contains the greatest number of oxygen atoms?
The first inorganic ion I think of is the peroxodisulfate ion,
Its structure is
An important polyatomic organic ion is ATP (adenosine triphosphate).
It contains 9 oxygen atoms in the phosphate groups plus 4 more from the ribose unit.
And we must not forget DNA.
A DNA strand can contain up to 2.5 million nucleotide pairs.
Each nucleotide contains 2 oxygen atoms in the phosphate and 3 from the deoxyribose.
With 12.5 million oxygen atoms plus those in the purine and pyrimidine bases, I suppose you could say that ATP is the polyatomic ion with the most oxygen atoms.