Oxoacids are acids that contain oxygen. Sulphur is known to form many oxoacids such as ${\mathrm{H}}_2{\mathrm{SO}}_4, {\mathrm{H}}_2{\mathrm{SO}}_3$, etc. In oxoacids of sulphur, sulphur exhibits a tetrahedral structure when coordinated to oxygen. Generally, oxoacids of sulphur contain at least one $\mathrm{S}=\mathrm{O}$ bond and one $\mathrm{S}-\mathrm{OH}$ bond. Terminal peroxide groups, terminal $\mathrm{S}=\mathrm{S}$, terminal and bridging oxygen atoms and chains of ${(-\mathrm{S}-)}_{\mathrm{n}}$ are also observed in addition to $\mathrm{S}=\mathrm{S}$ and $\mathrm{S}-\mathrm{OH}$. 

Among the following, the correct formula of Marshall's acid is