JEE Main 2017 — p Block Elements (Group 15, 16, 17 & 18) Question with Solution

                                                 Number of $\mathrm{\pi }$-bonds

${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_7=\mathrm{HO}-\underset{\mathrm{O}}{\stackrel{\mathrm{O}}{\underset{\left|\right|}{\stackrel{\left|\right|}{\mathrm{S}}}}}-\mathrm{O}-\underset{\mathrm{O}}{\stackrel{\mathrm{O}}{\underset{\left|\right|}{\stackrel{\left|\right|}{\mathrm{S}}}}}-\mathrm{OH}$       $4$

${\mathrm{H}}_2{\mathrm{So}}_4=\mathrm{OH}-\underset{\mathrm{O}}{\stackrel{\mathrm{O}}{\underset{\left|\right|}{\stackrel{\left|\right|}{\mathrm{S}}}}}-\mathrm{OH}$                      $2$

${\mathrm{H}}_2{\mathrm{SO}}_3=\mathrm{HO}-\underset{\mathrm{O}}{\underset{\left|\right|}{\stackrel{..}{\mathrm{S}}}}-\mathrm{OH}$                       $1$

Therefore, the correct sequence of decreasing number of pi-bonds is ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_7\left(4\right) >{\mathrm{H}}_2{\mathrm{SO}}_4 \left(2\right) >{\mathrm{H}}_2{\mathrm{SO}}_3\left(1\right)$. The numbers in bracket indicate the number of pi bonds.