What is the ratio of the molarities of po3 - 4 and hpo2 - 4 ions in a buffer solution having a ph of 10.92?

When we have Pka = 12.68 (missing in your question)

so by using H - H equation we can get the molarity ratio:

PH = Pka + ㏒ [conjugate base / weak acid]

when we have PH = 10.92

and Pka = 12.68

so by substitution:

10.92 = 12.68 + ㏒ [PO3-4]/[HPO2-4 ]

∴ [PO3-4]/[HPO2 - 4] = 0.017