How many of these acids have $\mathrm{S}-\mathrm{S}$ bonds?
${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_3,{\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_6,{\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_7,{\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_8,{\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_5,{\mathrm{H}}_2{\mathrm{S}}_{\mathrm{n}+2}{\mathrm{O}}_6$ (polythionic acid).

Solution

${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_3,{\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_6$ and ${\mathrm{H}}_2{\mathrm{S}}_{\mathrm{n}+2}{\mathrm{O}}_6$ have $\mathrm{S}-\mathrm{S}$ bond.

Hence, the correct answer is 3.