$H_2S_2O_7\,=$  $\begin{array}{*{20}{c}}
  {\begin{array}{*{20}{c}}
  {\,\,O\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,O\,} \\ 
  {\,||\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,||} 
\end{array}} \\ 
  {HO - S - O - S - OH} \\ 
  {||\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,||\,} \\ 
  {\,\,\,\,O\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,O\,\,\,\,} 
\end{array}$                       $4$

$H_2SO_4\,=$  $\begin{array}{*{20}{c}}
  {\begin{array}{*{20}{c}}
  O \\ 
  {||} 
\end{array}} \\ 
  {HO - S - OH} \\ 
  {||} \\ 
  O 
\end{array}$                        $2$

$H_2SO_3\,=$  $\begin{matrix}
   HO-\overset{\centerdot \,\,\centerdot }{\mathop{S}}\,-OH  \\
   ||  \\
   O  \\
\end{matrix}$                        $1$