Number of peroxy linkage in a ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_8$ (Marshal acid) molecule is :

Number of peroxy linkage in a ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_8$ (Marshal acid) molecule is 1.

There are 4 O−O bond present in ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_8$.

The O−O bond in a molecule forms the peroxy linkage. Caros acid is also known as peroxysulphuric acid, and as its name implies, it has a peroxy bond.