A 2.24 L sample (at STP) of ozonised oxygen (a mixture of $\mathrm{O}{}_2$ and $\mathrm{O}{}_3$ only) is passed through excess KI solution. The iodine liberated requires 38.4 mL of 0.500 M $\mathrm{Na}{}_2\mathrm{S}{}_2\mathrm{O}{}_3$ for complete reaction ($\mathrm{O}{}_3+2\mathrm{I}{}^{-}+\mathrm{H}{}_2\mathrm{O}\to \mathrm{I}{}_2+\mathrm{O}{}_2+2\mathrm{OH}{}^{-}$; $\mathrm{I}{}_2+2\mathrm{S}{}_2\mathrm{O}{}_3{}^{2-}\to 2\mathrm{I}{}^{-}+\mathrm{S}{}_4\mathrm{O}{}_6{}^{2-}$). Taking $\mathrm{O}$ = 16 and molar volume 22.4 L/mol at STP, calculate the mass percentage of ozone in the sample. Give the answer to two decimal places.

Numerical answer type, answer in %, tolerance 0.01.