Which of the following oxyacid does not contain $(\mathrm{S}-\mathrm{O}-\mathrm{S})$ linkage?

(P) ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_6$    (Q) ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_4$ 

(R) ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_3$ 

Pyrosulphuric acid H2S2O7 contains the S-O-S linkage which can be seen in the below structure.

In the given molecules none contains the S-O-S linkage.