Index of Hydrogen Deficiency for para-Toluenesulfonylchloride
You have to start from the general formula for the degree of unsaturation
$$DU = 1 + \frac{1}{2} \sum n_i(v_i-2),$$
where $n_i$ is the number of atoms with a valency of $v_i$.

For para-toluenesulfunylchloride ($\ce{C7H7SO2Cl}$) you will therefore arrive at
\begin{align}DU &amp;= 1 + \frac{1}{2}\Big[n_\ce{C}(4-2) + n_\ce{H}(1-2) + n_\ce{S}(6-2) + n_\ce{O}(2-2) + n_\ce{Cl}(1-2)\Big]\\
&amp;=1+\frac12\Big[7(4-2) + 7(1-2) + 1(6-2) + 2(2-2) +1(1-2)\\
&amp;=1 + \frac12\Big[14 -7 +4 +0 -1\Big]\\
&amp;=6,
\end{align}

because sulfur uses all six valence electrons in this case.